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1. What does the term “thermodynamics” literally mean?
ⓐ. Study of motion
ⓑ. Study of energy transformations
ⓒ. Study of equilibrium
ⓓ. Study of pressure and volume only
Correct Answer: Study of energy transformations
Explanation: Thermodynamics comes from Greek words “therme” (heat) and “dynamis” (power). It deals with energy transformations—especially between heat and work. It explains how energy is conserved and converted during physical and chemical processes.
2. Which of the following best defines the system in thermodynamics?
ⓐ. The part of the universe under study
ⓑ. Everything outside the laboratory
ⓒ. The entire universe
ⓓ. The surroundings of a reaction
Correct Answer: The part of the universe under study
Explanation: In thermodynamics, the system is the specific part of the universe chosen for study (e.g., a chemical reaction in a vessel). Everything else around it is called surroundings. The boundary separates them.
3. The rest of the universe excluding the system is called:
ⓐ. Isolated part
ⓑ. Environment
ⓒ. Surroundings
ⓓ. Boundary
Correct Answer: Surroundings
Explanation: The surroundings refer to everything outside the system that can exchange energy or matter with it. For example, if the system is a gas in a cylinder, the cylinder walls and the air around it are surroundings.
4. Which of the following is NOT a type of thermodynamic system?
ⓐ. Open system
ⓑ. Closed system
ⓒ. Isolated system
ⓓ. Dynamic system
Correct Answer: Dynamic system
Explanation: Thermodynamic systems are classified as open (exchange of matter and energy), closed (only energy exchange), and isolated (no exchange). “Dynamic system” is not a thermodynamic classification term.
5. What happens in an open system?
ⓐ. Energy only is exchanged
ⓑ. Matter only is exchanged
ⓒ. Neither matter nor energy is exchanged
ⓓ. Both matter and energy are exchanged
Correct Answer: Both matter and energy are exchanged
Explanation: In an open system, both energy (heat, work) and matter can cross the boundary. Example: an open beaker of water allows water vapor (matter) and heat to escape into surroundings.
6. In thermodynamics, what are state variables?
ⓐ. Variables that depend on the path followed
ⓑ. Variables that depend only on initial and final states
ⓒ. Variables that depend on the rate of reaction
ⓓ. Variables that change only with temperature
Correct Answer: Variables that depend only on initial and final states
Explanation: State variables (like pressure (P), volume (V), temperature (T), internal energy (U)) describe the system’s condition. Their change depends only on the initial and final states, not on the path taken.
7. Which of the following is an extensive property?
ⓐ. Temperature
ⓑ. Pressure
ⓒ. Volume
ⓓ. Density
Correct Answer: Volume
Explanation: Extensive properties depend on the amount of substance (mass, volume, energy). Intensive properties like temperature, pressure, and density are independent of quantity. Doubling the system doubles volume but not temperature.
8. Which statement correctly explains the First Law of Thermodynamics?
ⓐ. Energy can be created and destroyed.
ⓑ. Energy can neither be created nor destroyed, only transformed.
ⓒ. Energy is lost during reactions.
ⓓ. Internal energy always decreases.
Correct Answer: Energy can neither be created nor destroyed, only transformed.
Explanation: The First Law, also called the Law of Energy Conservation, states that the total energy of an isolated system remains constant. Mathematically, ( \Delta U = q + w ), where (q) is heat and (w) is work.
9. Which of the following is a spontaneous process?
ⓐ. Water flowing uphill
ⓑ. Heat flowing from cold to hot body
ⓒ. Ice melting at room temperature
ⓓ. Compression of gas without work
Correct Answer: Ice melting at room temperature
Explanation: Spontaneous processes occur naturally without external help. Ice melts at room temperature because the entropy (randomness) increases, and the process leads to a lower Gibbs free energy (( \Delta G < 0 )).
10. What is the SI unit of energy commonly used in thermodynamics?
ⓐ. Calorie
ⓑ. Erg
ⓒ. Joule
ⓓ. Watt
Correct Answer: Joule
Explanation: The SI unit of energy is the joule (J). (1 \text{ J} = 1 \text{ kg·m}^2\text{s}^{-2}). Although calorie is sometimes used ((1 \text{ cal} = 4.184 \text{ J})), the joule is the standard SI unit for energy, work, and heat.
11. What is meant by a thermodynamic system?
ⓐ. The entire universe where changes occur
ⓑ. The specific part of the universe chosen for study
ⓒ. The total energy of all materials present
ⓓ. The boundary separating two substances
Correct Answer: The specific part of the universe chosen for study
Explanation: In thermodynamics, a system is that specific portion of the universe which is selected for analysis. It may be a chemical reaction, a gas in a cylinder, or even a single phase of matter. The system is separated from the surroundings by a boundary, and any energy or matter exchanges occur through this boundary. For example, a hot cup of tea can be considered a system that interacts with air (surroundings) through heat exchange.
12. What are surroundings in thermodynamics?
ⓐ. The substances inside the system
ⓑ. Only the immediate air around a system
ⓒ. Everything outside the system that can interact with it
ⓓ. The walls of the container
Correct Answer: Everything outside the system that can interact with it
Explanation: Surroundings are everything external to the system that can exchange energy or matter with it. The system and surroundings together form the universe. For instance, if a reaction occurs in a beaker, the beaker, air, and laboratory environment all form the surroundings. This concept helps in studying how energy flows between the system and its environment.
13. Which of the following correctly describes the boundary between system and surroundings?
ⓐ. It is always a fixed, rigid surface
ⓑ. It can be real or imaginary depending on the situation
ⓒ. It allows no exchange between system and surroundings
ⓓ. It only separates gases
Correct Answer: It can be real or imaginary depending on the situation
Explanation: The boundary is an interface that separates the system from its surroundings. It can be real, like the wall of a container, or imaginary, such as an assumed surface around a reaction in open air. The type of boundary determines whether energy and matter can pass through it. Understanding the boundary is crucial for classifying systems as open, closed, or isolated.
14. What is meant by an isolated system?
ⓐ. A system that exchanges energy but not matter
ⓑ. A system that exchanges both energy and matter
ⓒ. A system that exchanges neither energy nor matter
ⓓ. A system that only exchanges matter
Correct Answer: A system that exchanges neither energy nor matter
Explanation: An isolated system is completely cut off from its surroundings. No transfer of heat, work, or matter occurs across its boundary. A perfect example is a thermos flask designed to minimize heat loss or gain. Though in reality, no system can be perfectly isolated, this concept is ideal for studying conservation of energy within a system.
15. Which example best represents an open system?
ⓐ. A sealed pressure cooker
ⓑ. A hot cup of coffee in an open mug
ⓒ. A gas in a closed piston
ⓓ. An insulated icebox
Correct Answer: A hot cup of coffee in an open mug
Explanation: In an open system, both matter and energy can be exchanged with surroundings. The coffee can lose heat to air and water vapor can escape into the surroundings. In contrast, a closed system like a sealed container allows only energy transfer, not matter transfer, and an isolated system allows neither.
16. A closed system is one in which:
ⓐ. Matter can enter or leave freely but not energy
ⓑ. Both matter and energy can move across the boundary
ⓒ. Only energy can be exchanged, not matter
ⓓ. Neither matter nor energy can be exchanged
Correct Answer: Only energy can be exchanged, not matter
Explanation: In a closed system, energy (like heat or work) can cross the boundary, but matter cannot. For example, a gas contained in a piston-cylinder arrangement is a closed system because heat can flow and work can be done by or on the gas, but no molecules of gas leave or enter the container.
17. Which of the following statements is correct about system and surroundings?
ⓐ. System and surroundings are always the same
ⓑ. The sum of system and surroundings forms the universe
ⓒ. Only surroundings are affected by thermodynamic changes
ⓓ. The system cannot change during a process
Correct Answer: The sum of system and surroundings forms the universe
Explanation: In thermodynamics, the system and its surroundings together constitute the universe. Any energy lost by the system is gained by the surroundings and vice versa, maintaining overall energy conservation. This relationship is fundamental in the first law of thermodynamics which states that energy can neither be created nor destroyed.
18. Which of the following is not a correct example of a system?
ⓐ. A reaction mixture in a test tube
ⓑ. Boiling water in an open pot
ⓒ. Air enclosed in a cylinder with a piston
ⓓ. The entire atmosphere of Earth
Correct Answer: The entire atmosphere of Earth
Explanation: The entire atmosphere cannot be treated as a single thermodynamic system because it is too vast and non-uniform. Systems are defined as finite, measurable parts of the universe under observation, like a portion of air or a specific reaction vessel. Thus, the other options represent valid systems with definable boundaries.
19. What is meant by the term “universe” in thermodynamics?
ⓐ. Only the surroundings
ⓑ. The earth and atmosphere
ⓒ. The system plus its surroundings
ⓓ. Only the energy within the system
Correct Answer: The system plus its surroundings
Explanation: The thermodynamic universe includes both the system under study and everything external to it (the surroundings). The concept ensures that when analyzing energy changes, the total energy of the universe remains constant even though energy can flow between the system and surroundings.
20. Which of the following statements about system and surroundings is false?
ⓐ. The system is the part of the universe under study
ⓑ. The surroundings can never affect the system
ⓒ. The system and surroundings together make up the universe
ⓓ. The boundary separates the system from its surroundings
Correct Answer: The surroundings can never affect the system
Explanation: This statement is false because surroundings can influence the system through energy or matter exchange. For example, heating a container of gas changes the gas’s temperature due to energy flow from the surroundings. In thermodynamics, the interaction between system and surroundings is key to understanding heat, work, and energy transfer.
21. What is meant by a boundary in thermodynamics?
ⓐ. The layer that divides the universe into two equal parts
ⓑ. The surface separating the system from its surroundings
ⓒ. The point at which reactions occur inside the system
ⓓ. The fixed wall of the container holding the substance
Correct Answer: The surface separating the system from its surroundings
Explanation: A boundary is an interface that separates the system from the surroundings. It defines the limits of the system. The boundary can be visible like the wall of a container or invisible like an imagined surface enclosing an open flame. It determines how matter or energy can move between the system and its surroundings. Without defining the boundary, it is impossible to describe or analyze any thermodynamic process properly.
22. Which of the following is a real boundary?
ⓐ. The surface of water in a glass
ⓑ. The surface of an imaginary sphere around a flame
ⓒ. A mathematical plane separating two gases
ⓓ. A hypothetical line drawn through air
Correct Answer: The surface of water in a glass
Explanation: A real boundary is a physically observable or tangible surface that separates the system from its surroundings. For instance, the glass wall or water surface in a beaker is a real boundary because it can be touched or seen. It clearly defines where the system ends and surroundings begin. Real boundaries are commonly found in laboratory setups involving containers, pistons, or flasks.
23. What is an imaginary boundary in thermodynamics?
ⓐ. A physical wall that restricts all movement
ⓑ. A conceptual surface drawn to define a system
ⓒ. A barrier that reflects heat
ⓓ. A conducting surface made of metal
Correct Answer: A conceptual surface drawn to define a system
Explanation: An imaginary boundary is not physically real but assumed for convenience. It helps scientists define systems that are open to surroundings. For example, when studying the air around a flying bird or an explosion, no real wall exists, but we can imagine a closed surface that encloses the system for analysis. Imaginary boundaries help apply thermodynamic laws even to open and moving systems.
24. In a gas cylinder with a movable piston, the piston surface acts as which type of boundary?
ⓐ. Imaginary boundary
ⓑ. Fixed boundary
ⓒ. Real and movable boundary
ⓓ. Isolated boundary
Correct Answer: Real and movable boundary
Explanation: The piston surface in a gas cylinder is a real boundary because it physically exists and separates the gas (system) from the external environment (surroundings). It is also movable since it can shift up or down when pressure changes. This movement allows work to be done on or by the system, which is a fundamental concept in thermodynamic processes such as expansion and compression.
25. The boundary of a thermos flask containing hot tea can be considered as:
ⓐ. Real and insulated boundary
ⓑ. Imaginary and movable boundary
ⓒ. Open boundary
ⓓ. Rigid but not real boundary
Correct Answer: Real and insulated boundary
Explanation: The walls of a thermos flask are real and provide insulation, which minimizes energy exchange between the hot tea (system) and surroundings. Since the wall exists physically and prevents both heat and matter flow, it is a real and insulated boundary. Such systems closely approximate isolated systems where no interaction with the environment occurs.
26. What is the main difference between a real and imaginary boundary?
ⓐ. Real boundaries are always open, imaginary ones are closed
ⓑ. Real boundaries exist physically, imaginary ones are conceptual
ⓒ. Imaginary boundaries are made of metals, real ones are not
ⓓ. Real boundaries cannot conduct heat, imaginary ones can
Correct Answer: Real boundaries exist physically, imaginary ones are conceptual
Explanation: A real boundary can be observed, touched, or measured, like the wall of a vessel or surface of a liquid. Imaginary boundaries are hypothetical and used to enclose systems without physical walls, such as air currents or sound waves. Both are essential in thermodynamics to analyze how matter and energy move across different types of systems.
27. The surface separating gas inside a balloon from the external air is a:
ⓐ. Fixed imaginary boundary
ⓑ. Flexible real boundary
ⓒ. Rigid imaginary boundary
ⓓ. Invisible insulated boundary
Correct Answer: Flexible real boundary
Explanation: The balloon’s rubber wall is a real and flexible boundary. It physically exists and can stretch or contract depending on internal pressure. This flexibility allows the gas inside to expand or compress, resulting in work being done by or on the system. The energy transfer occurs in the form of work done by pressure-volume changes.
28. Which of the following is an example where an imaginary boundary is most useful?
ⓐ. A gas in a sealed metal container
ⓑ. Liquid boiling in a pressure cooker
ⓒ. Ice melting in a closed box
ⓓ. A chemical reaction taking place in open air
Correct Answer: A chemical reaction taking place in open air
Explanation: When a process occurs in open air, such as combustion or evaporation, there is no physical container. In such cases, an imaginary boundary is drawn to define the system region for thermodynamic study. This allows calculation of heat and work exchange even though the physical separation between system and surroundings does not exist in reality.
29. What determines whether a boundary allows transfer of matter or energy?
ⓐ. The shape of the system
ⓑ. The material or nature of the boundary
ⓒ. The size of the surroundings
ⓓ. The speed of the reaction
Correct Answer: The material or nature of the boundary
Explanation: Whether matter or energy can cross a boundary depends on its physical nature. For instance, a metal wall allows heat flow (conducting boundary), while a perfectly insulated wall does not (adiabatic boundary). Similarly, an open surface permits matter exchange while a sealed wall restricts it. Therefore, understanding boundary type is key to classifying a system as open, closed, or isolated.
30. A system defined by an imaginary boundary is often used when:
ⓐ. The process occurs without any walls or containers
ⓑ. The reaction is at constant volume
ⓒ. The system has a fixed amount of matter
ⓓ. The system is completely insulated
Correct Answer: The process occurs without any walls or containers
Explanation: Imaginary boundaries are assumed in cases where no physical boundaries exist, such as explosions, gas diffusion, or air currents. It helps to define the limits of the system mathematically so that laws of thermodynamics can be applied. By drawing an imaginary surface around the region of interest, scientists can study how heat, work, and mass interact with the surroundings even in open-space processes.
31. What is a reversible process in thermodynamics?
ⓐ. A process that occurs naturally without any control
ⓑ. A process that can be reversed by an infinitesimal change in a variable
ⓒ. A process that happens very quickly
ⓓ. A process that only occurs at constant pressure
Correct Answer: A process that can be reversed by an infinitesimal change in a variable
Explanation: A reversible process is an idealized process that proceeds infinitely slowly, allowing the system to remain in equilibrium at every stage. If any variable such as pressure or temperature is slightly altered, the process can be exactly reversed. Though no real process is perfectly reversible, this concept helps in understanding maximum efficiency in thermodynamic systems.
32. Which of the following is an irreversible process?
ⓐ. Slow compression of gas in a piston
ⓑ. Reversible heat exchange between two bodies
ⓒ. Melting of ice at 0°C under controlled temperature
ⓓ. Expansion of gas into vacuum
Correct Answer: Expansion of gas into vacuum
Explanation: When gas expands freely into a vacuum, it does not return to its original state even if external conditions are restored. The process is fast and occurs without equilibrium, so it is irreversible. Real-world processes, such as frictional motion or spontaneous chemical reactions, are generally irreversible due to energy loss and non-equilibrium states.
33. In an isothermal process, which of the following remains constant?
ⓐ. Pressure
ⓑ. Internal energy
ⓒ. Volume
ⓓ. Temperature
Correct Answer: Temperature
Explanation: In an isothermal process, the temperature of the system remains constant throughout. Since temperature is constant, there is no change in internal energy (ΔU = 0 for ideal gases). The heat supplied to the system is completely converted into work. A slow expansion of an ideal gas in a thermostat bath is a good example of an isothermal process.
34. What happens to the internal energy of an ideal gas during an isothermal process?
ⓐ. It increases with expansion
ⓑ. It decreases with compression
ⓒ. It remains constant
ⓓ. It doubles when pressure doubles
Correct Answer: It remains constant
Explanation: For an ideal gas, internal energy depends only on temperature. In an isothermal process, since temperature is constant, internal energy (ΔU) does not change. Therefore, any heat absorbed by the system (q) is exactly equal to the work done by the system (w), expressed as q = w.
35. What is meant by an adiabatic process?
ⓐ. A process that takes place at constant temperature
ⓑ. A process in which heat is neither gained nor lost by the system
ⓒ. A process that occurs only in open systems
ⓓ. A process that requires continuous heat supply
Correct Answer: A process in which heat is neither gained nor lost by the system
Explanation: In an adiabatic process, the system is thermally insulated so that no heat exchange (q = 0) occurs with the surroundings. Any change in internal energy is entirely due to work done on or by the system. Adiabatic expansion of air in a piston is a common example, where temperature drops due to work done by the gas without heat exchange.
36. Which of the following correctly describes an isothermal expansion of an ideal gas?
ⓐ. Pressure remains constant while volume changes
ⓑ. Volume and pressure both remain constant
ⓒ. Temperature remains constant and heat absorbed equals work done
ⓓ. No work is done since temperature does not change
Correct Answer: Temperature remains constant and heat absorbed equals work done
Explanation: During isothermal expansion, the system absorbs heat from the surroundings, but this energy is completely used to do work. Hence, there is no change in internal energy (ΔU = 0). The relation for work done is W = nRT ln(V₂/V₁). This process is often represented by a hyperbolic curve on a P–V diagram.
37. During adiabatic expansion of an ideal gas:
ⓐ. Temperature increases
ⓑ. Temperature decreases
ⓒ. Temperature remains constant
ⓓ. Pressure remains constant
Correct Answer: Temperature decreases
Explanation: In adiabatic expansion, the gas does work at the expense of its internal energy, causing its temperature to fall. Since no heat enters the system (q = 0), the internal energy change equals the negative of the work done. The relationship between pressure and volume for adiabatic processes is given by ( PV^{\gamma} = \text{constant} ), where γ is the heat capacity ratio (Cp/Cv).
38. Which of the following conditions must hold true for a process to be reversible?
ⓐ. The system must pass through a series of equilibrium states
ⓑ. The process must occur rapidly
ⓒ. The process must involve friction
ⓓ. The system must exchange energy freely
Correct Answer: The system must pass through a series of equilibrium states
Explanation: A reversible process proceeds so slowly that the system remains infinitesimally close to equilibrium at every instant. Because of this, the process can be exactly reversed without any loss of energy. Real processes, which involve friction, turbulence, or sudden changes, cannot meet this condition and are therefore irreversible.
39. Which of the following equations represents an adiabatic process?
ⓐ. PV = constant
ⓑ. PV² = constant
ⓒ. PV^γ = constant
ⓓ. P = constant
Correct Answer: PV^γ = constant
Explanation: For an adiabatic process, pressure and volume are related by ( PV^{\gamma} = \text{constant} ), where γ = Cp/Cv (ratio of specific heats). This equation shows that when the gas expands (V increases), pressure decreases more rapidly than in an isothermal process. This relationship is derived from the first law of thermodynamics when q = 0.
40. Which process among the following involves heat exchange with surroundings?
ⓐ. Adiabatic process
ⓑ. Isothermal process
ⓒ. Isolated process
ⓓ. Free expansion
Correct Answer: Isothermal process
Explanation: In an isothermal process, heat exchange occurs between the system and surroundings to maintain a constant temperature. For example, when gas expands slowly in contact with a heat reservoir, it absorbs heat to compensate for the work done. In contrast, adiabatic and isolated processes do not involve any heat transfer. Thus, heat exchange is the characteristic feature of isothermal processes.
41. What is an open system in thermodynamics?
ⓐ. A system that exchanges only energy with surroundings
ⓑ. A system that exchanges both matter and energy with surroundings
ⓒ. A system that exchanges neither energy nor matter
ⓓ. A system that remains completely isolated from the environment
Correct Answer: A system that exchanges both matter and energy with surroundings
Explanation: An open system allows both energy (in the form of heat or work) and matter to cross its boundary. A boiling pot of water is a typical example where steam (matter) escapes and heat (energy) is exchanged with the surroundings. Open systems are common in natural and industrial processes, such as human bodies or engines, where continuous input and output occur.
42. Which of the following is the best example of an open system?
ⓐ. Air enclosed in a sealed piston
ⓑ. Boiling water in an open vessel
ⓒ. Ice cubes in a thermos flask
ⓓ. Gas stored in a closed cylinder
Correct Answer: Boiling water in an open vessel
Explanation: In an open vessel, both steam (matter) and heat (energy) are exchanged with the surroundings. The system constantly interacts with the environment, making it open. The other examples like a sealed piston or a thermos flask restrict either matter or both, hence are not open systems. Such open systems are vital in studying processes that are dynamic and non-isolated.
43. Which of the following characteristics does not apply to an open system?
ⓐ. Exchange of matter with surroundings
ⓑ. Exchange of energy with surroundings
ⓒ. Total isolation from environment
ⓓ. Variable mass and composition
Correct Answer: Total isolation from environment
Explanation: An open system is never isolated; it always interacts with its surroundings. Both matter and energy can enter or leave, which results in changing composition or mass. For example, in photosynthesis, plants exchange gases and absorb solar energy, showing that open systems are dynamic and continually changing.
44. A human body can be considered as which type of system?
ⓐ. Closed system
ⓑ. Isolated system
ⓒ. Open system
ⓓ. Adiabatic system
Correct Answer: Open system
Explanation: The human body is an open system because it continuously exchanges matter and energy with its surroundings. We take in oxygen and food (matter), release carbon dioxide and wastes, and exchange heat with the environment. These exchanges allow vital biological processes to occur, maintaining the system’s balance and functionality.
45. Which of the following processes occurs in an open system?
ⓐ. Gas compressed in a sealed piston
ⓑ. Water evaporating from an open container
ⓒ. Heat trapped in a closed thermos
ⓓ. Energy transfer in a completely insulated chamber
Correct Answer: Water evaporating from an open container
Explanation: When water evaporates from an open container, matter (water vapor) escapes and energy (heat) is absorbed from surroundings. Hence, both matter and energy cross the boundary, fulfilling the conditions of an open system. The process is dynamic, and temperature, mass, and volume can all vary with time.
46. Why are industrial chemical reactors considered open systems?
ⓐ. Because they exchange neither energy nor matter
ⓑ. Because they only absorb energy
ⓒ. Because they exchange both reactants and products with surroundings
ⓓ. Because they are completely sealed during reactions
Correct Answer: Because they exchange both reactants and products with surroundings
Explanation: In industrial reactors, raw materials (reactants) are fed into the system and products are continuously removed. Additionally, heat is supplied or removed to maintain desired reaction conditions. These ongoing exchanges of matter and energy make chemical reactors typical open systems, essential for continuous production in industries.
47. Which of the following statements about open systems is correct?
ⓐ. Their mass remains constant
ⓑ. They are always insulated
ⓒ. They are always at thermal equilibrium
ⓓ. They allow continuous inflow and outflow of matter and energy
Correct Answer: They allow continuous inflow and outflow of matter and energy
Explanation: Open systems maintain dynamic equilibrium by allowing continuous flow of substances and energy across their boundaries. For example, in an open cooling tower, water and air interact constantly while heat is released. This continuous exchange enables such systems to operate steadily even under non-equilibrium conditions.
48. In an open system, internal energy can change due to:
ⓐ. Only mechanical work
ⓑ. Only heat exchange
ⓒ. Both heat and mass transfer
ⓓ. Neither heat nor mass transfer
Correct Answer: Both heat and mass transfer
Explanation: In an open system, internal energy changes because both heat and matter cross the boundary. When matter enters or leaves, it carries internal energy with it. Thus, total internal energy change (ΔU) depends on the heat added, work done, and the enthalpy carried by incoming and outgoing matter. This concept is essential in analyzing open systems like turbines or compressors.
49. In thermodynamics, the earth’s atmosphere can be regarded as:
ⓐ. A closed system
ⓑ. An open system
ⓒ. An isolated system
ⓓ. A static system
Correct Answer: An open system
Explanation: The atmosphere constantly exchanges both matter and energy with outer space and the surface of the earth. Solar radiation enters, heat radiates out, and gases mix continuously. Hence, it behaves as an open system. This exchange is responsible for weather patterns, climate balance, and the earth’s energy flow.
50. In an open system like a steam turbine, what type of interaction occurs with surroundings?
ⓐ. Only heat exchange occurs
ⓑ. Only work is done
ⓒ. Both energy and mass are transferred continuously
ⓓ. No interaction occurs at all
Correct Answer: Both energy and mass are transferred continuously
Explanation: In a steam turbine, steam enters at high pressure and exits at lower pressure, performing work on the turbine blades. Thus, both energy (work and heat) and matter (steam flow) are exchanged with surroundings. This continuous interaction defines open systems and allows turbines to convert thermal energy into mechanical energy efficiently.
51. Which statement best defines a closed system?
ⓐ. A system that exchanges both matter and energy with surroundings
ⓑ. A system that exchanges only matter with surroundings
ⓒ. A system that exchanges neither matter nor energy with surroundings
ⓓ. A system that exchanges energy but not matter with surroundings
Correct Answer: A system that exchanges energy but not matter with surroundings
Explanation: In a closed system, the boundary prevents matter transfer but allows energy transfer as heat or work. Thus mass of the system remains constant while quantities like internal energy can change. A sealed metal vessel that can be heated from outside is a typical example. Open systems exchange both matter and energy, while isolated systems exchange neither.
52. Which setup is the best example of a closed system?
ⓐ. Gas confined in a sealed piston–cylinder with a movable piston
ⓑ. Water boiling in an open pan on a stove
ⓒ. A room with open windows and a fan running
ⓓ. A balloon with a small hole releasing air
Correct Answer: Gas confined in a sealed piston–cylinder with a movable piston
Explanation: In a sealed piston–cylinder, gas cannot enter or leave, so mass is fixed, but the piston can move, allowing work, and the cylinder wall can permit heat flow. Hence it is a closed system. An open pan and a leaking balloon exchange matter, so they are open systems. A room with open windows also exchanges air (matter), making it open.
53. Which property is necessarily constant for any closed system undergoing any process?
ⓐ. Temperature
ⓑ. Mass of the system
ⓒ. Pressure
ⓓ. Volume
Correct Answer: Mass of the system
Explanation: By definition, a closed system does not permit mass transfer across its boundary, so the amount of substance inside remains constant. Temperature, pressure, and volume can change depending on heat and work interactions. For instance, compression in a piston changes pressure and volume even though no mass enters or leaves.
54. In thermodynamics, which statement about a closed system is always true?
ⓐ. It cannot exchange heat with surroundings
ⓑ. It must have constant volume at all times
ⓒ. Its composition (number of moles) remains fixed
ⓓ. Its internal energy remains constant
Correct Answer: Its composition (number of moles) remains fixed
Explanation: With no matter crossing the boundary, the number of moles of each species in a closed system is fixed during the process. Heat and work interactions can still alter internal energy, and depending on the boundary (rigid or movable), volume may or may not change. Thermal interaction depends on whether the wall is diathermic or adiabatic.
55. For a closed system, the first law is written as:
ⓐ. ( \Delta U = q + w )
ⓑ. ( \Delta U = q – w ) where ( w ) is work done by the system
ⓒ. ( \Delta U = \Delta H – P\Delta V )
ⓓ. ( \Delta U = 0 ) for all processes
Correct Answer: ( \Delta U = q + w )
Explanation: In chemistry sign convention, (q) is heat absorbed by the system and (w) is work done on the system. Since no mass crosses the boundary in a closed system, flow terms are absent. Thus the energy balance reduces to ( \Delta U = q + w ). Option B uses an alternate sign convention for (w) (work by the system negative), but as stated, A is the standard chemistry form.
56. A sealed metal container of gas is heated on a flame. Which description fits the boundary and transfers?
ⓐ. Imaginary boundary; both heat and mass cross
ⓑ. Adiabatic boundary; only work crosses
ⓒ. Rigid adiabatic boundary; neither heat nor work crosses
ⓓ. Real diathermic boundary; heat can cross but no mass crosses
Correct Answer: Real diathermic boundary; heat can cross but no mass crosses
Explanation: The metal wall is a real boundary that allows heat conduction (diathermic) yet prevents mass flow because the container is sealed. Work transfer may occur only if the boundary is deformable; a rigid container prevents (P!-!V) work. In an adiabatic wall, (q=0), which is not the case for a container on a flame. Thus D captures the correct behavior.
57. In a closed system, 500 J of heat is supplied and the system does 200 J of work on the surroundings. What is ( \Delta U )?
ⓐ. ( -700 ) J
ⓑ. ( -300 ) J
ⓒ. ( +300 ) J
ⓓ. ( +700 ) J
Correct Answer: ( +300 ) J
Explanation: Using the chemistry convention ( \Delta U = q + w ), with (q = +500) J (heat absorbed). Work done by the system corresponds to (w = -200) J (since (w) is work on the system). Therefore ( \Delta U = 500 + (-200) = +300 ) J. Mass does not cross the boundary, so no flow-energy terms are present in this closed-system energy balance.
58. Which of the following is not a closed system?
ⓐ. Air in a sealed, movable piston exchanging heat with a bath
ⓑ. Water boiling vigorously in an open pot
ⓒ. Ice sealed in a well-insulated box
ⓓ. Gas sealed in a cylinder undergoing slow compression
Correct Answer: Water boiling vigorously in an open pot
Explanation: An open pot allows vapor (matter) to escape while heat flows from the burner, so it is an open system. The other cases prevent mass exchange: a sealed piston (closed), sealed ice box (closed or nearly isolated if well insulated), and a sealed cylinder under compression (closed). In closed systems, only energy crosses the boundary, not matter.
59. One mole of an ideal gas is heated in a closed, rigid container from (T_1) to (T_2). What is the boundary work (W)?
ⓐ. ( W = nR(T_2 – T_1) )
ⓑ. ( W = -\int P,dV \neq 0 ) because pressure changes
ⓒ. ( W = P\Delta V ) which equals ( nR(T_2 – T_1) )
ⓓ. ( W = 0 ) because ( \Delta V = 0 )
Correct Answer: ( W = 0 ) because ( \Delta V = 0 )
Explanation: In a rigid container, volume is constant, so (dV=0) and the boundary work (W = \int P,dV = 0). Temperature and pressure can change due to heat input, but without volume change, no (P!-!V) work is done. Since the system is closed, mass remains constant and only internal energy changes (( \Delta U = q )) for this process.
60. A closed system with adiabatic walls is compressed so that 800 J of work is done on the system. The heat transfer is zero. What is ( \Delta U )?
ⓐ. ( +800 ) J
ⓑ. ( -800 ) J
ⓒ. ( 0 ) J
ⓓ. Cannot be determined without temperature
Correct Answer: ( +800 ) J
Explanation: For a closed adiabatic process, (q=0). Using ( \Delta U = q + w ) with work done on the system (w=+800) J, we get ( \Delta U = 0 + 800 = +800 ) J. Internal energy increases because the surroundings do work on the system. Temperature of an ideal gas would rise, but its exact value is not needed to compute ( \Delta U ).
61. What is an isolated system in thermodynamics?
ⓐ. A system that exchanges only energy with surroundings
ⓑ. A system that exchanges only matter with surroundings
ⓒ. A system that exchanges both matter and energy with surroundings
ⓓ. A system that exchanges neither matter nor energy with surroundings
Correct Answer: A system that exchanges neither matter nor energy with surroundings
Explanation: An isolated system is completely cut off from its surroundings. No mass or energy crosses its boundary. The total energy and mass of the system remain constant. Although a perfectly isolated system is ideal, practical examples include an insulated thermos flask or the universe itself, where external interaction is absent.
62. Which of the following is the best example of an isolated system?
ⓐ. Water boiling in an open pot
ⓑ. Hot tea kept in a thermos flask
ⓒ. A piston-cylinder with movable piston
ⓓ. A refrigerator running in a kitchen
Correct Answer: Hot tea kept in a thermos flask
Explanation: A thermos flask is designed to minimize both heat and matter exchange with the surroundings. Its double walls, vacuum insulation, and tight cap reduce heat loss, making it a near-perfect isolated system. However, no system can be 100% isolated forever, as small amounts of heat leakage eventually occur.
63. Which condition must be satisfied for a system to be considered isolated?
ⓐ. No heat exchange, no work interaction, and no mass transfer
ⓑ. Only pressure remains constant
ⓒ. Volume remains constant while energy flows
ⓓ. Temperature changes continuously
Correct Answer: No heat exchange, no work interaction, and no mass transfer
Explanation: For an isolated system, all three types of interaction—heat transfer, work transfer, and mass transfer—are absent. The system’s total energy stays fixed. The universe itself is an example of an isolated system because there is nothing outside it to exchange energy or matter with. Isolated systems help study energy conservation principles clearly.
64. In an isolated system, what happens to the total energy?
ⓐ. It keeps increasing
ⓑ. It keeps decreasing
ⓒ. It remains constant
ⓓ. It fluctuates with time
Correct Answer: It remains constant
Explanation: According to the first law of thermodynamics, energy can neither be created nor destroyed. Since an isolated system has no exchange with surroundings, its total energy stays constant. Internal transformations may occur, converting one form of energy to another (like potential to kinetic), but the total remains unchanged.
65. A perfectly insulated and sealed container of gas is an example of which system?
ⓐ. Open system
ⓑ. Closed system
ⓒ. Isolated system
ⓓ. Reversible system
Correct Answer: Isolated system
Explanation: A sealed container that does not allow heat, work, or matter transfer acts as an isolated system. Even if temperature or pressure changes occur inside, no energy crosses the boundary. Practically, perfect insulation is not achievable, but such systems approximate isolated behavior and are used to study energy conservation laws.
66. Which of the following statements about isolated systems is incorrect?
ⓐ. Their mass remains constant
ⓑ. They cannot exchange energy
ⓒ. Their total energy may increase with time
ⓓ. Their boundary is perfectly adiabatic
Correct Answer: Their total energy may increase with time
Explanation: In an isolated system, total energy cannot increase because no energy enters or leaves. The internal energy distribution may change due to internal processes, but the total remains fixed. Option C is incorrect since it violates energy conservation. The boundaries of such systems are usually adiabatic, preventing heat flow.
67. Which thermodynamic law is directly demonstrated by an isolated system?
ⓐ. Zeroth law
ⓑ. First law
ⓒ. Second law
ⓓ. Third law
Correct Answer: First law
Explanation: The first law of thermodynamics, or the law of conservation of energy, is best illustrated through an isolated system. Since no energy enters or leaves, the total energy within remains constant. Internal energy may convert from one form to another, but the overall amount is preserved, proving energy conservation.
68. When two isolated systems are brought in contact and allowed to interact, the combined system:
ⓐ. Remains isolated from the rest of the universe
ⓑ. Becomes an open system
ⓒ. Exchanges energy with surroundings freely
ⓓ. Becomes a closed system
Correct Answer: Remains isolated from the rest of the universe
Explanation: When two isolated systems interact with each other but not with the external universe, the combination still remains isolated overall. Energy or matter may transfer between the two subsystems, but their total within the combined boundary remains constant. This principle is key to understanding energy conservation on a universal scale.
69. Which of the following processes occurs in an isolated system?
ⓐ. Heat flows from system to surroundings
ⓑ. Energy transfer continues indefinitely
ⓒ. The system undergoes internal energy redistribution only
ⓓ. The system exchanges heat but not matter
Correct Answer: The system undergoes internal energy redistribution only
Explanation: Inside an isolated system, energy can change forms or move internally but cannot leave or enter the boundary. For example, in an isolated gas mixture, energy may transfer between molecules until equilibrium is reached. However, no net heat or mass crosses the system boundary.
70. The universe as a whole is considered an isolated system because:
ⓐ. It continuously gains energy from outside
ⓑ. There is no surrounding outside the universe
ⓒ. It constantly exchanges energy with other galaxies
ⓓ. Its total energy decreases due to entropy
Correct Answer: There is no surrounding outside the universe
Explanation: The universe includes everything that exists; therefore, it has no surroundings beyond itself. No energy or matter can enter or leave it, satisfying the definition of an isolated system. Internal energy transformations still occur, but the total energy remains constant, perfectly illustrating the first law of thermodynamics.
71. In thermodynamics, what does the term “work” refer to?
ⓐ. The transfer of matter between system and surroundings
ⓑ. The energy transfer that results from a temperature difference
ⓒ. The energy transfer that takes place when an external force moves the boundary of a system
ⓓ. The total heat content of a system
Correct Answer: The energy transfer that takes place when an external force moves the boundary of a system
Explanation: In thermodynamics, work is the energy transferred when the system’s boundary moves under an external force. For example, in a gas-piston setup, gas expansion pushes the piston upward, doing work on the surroundings. Work is a mode of energy transfer distinct from heat, which occurs due to temperature difference. Both affect the internal energy of the system.
72. Which of the following is an example of work done by a thermodynamic system?
ⓐ. Heat absorbed by a gas from a heater
ⓑ. A gas expanding and pushing a piston upward
ⓒ. Mixing of two liquids at constant temperature
ⓓ. Heat exchange between two bodies
Correct Answer: A gas expanding and pushing a piston upward
Explanation: When a gas expands against an external pressure, it exerts force on the piston and displaces it. The system performs work on the surroundings. The amount of work is given by ( w = -P_{\text{ext}} \Delta V ), where ( \Delta V ) is the volume change. Negative sign indicates work done by the system, following chemistry convention.
73. What is the mathematical expression for work done during expansion or compression of a gas at constant external pressure?
ⓐ. ( w = P \times V )
ⓑ. ( w = -P_{\text{ext}} \Delta V )
ⓒ. ( w = nRT )
ⓓ. ( w = q + \Delta U )
Correct Answer: ( w = -P_{\text{ext}} \Delta V )
Explanation: Work in expansion or compression is calculated by ( w = -P_{\text{ext}} \Delta V ). The negative sign arises because when a gas expands (( \Delta V > 0 )), it does work on surroundings, resulting in a loss of internal energy. If the gas is compressed (( \Delta V < 0 )), work is done on the gas, increasing its energy.
74. What happens to the work done when a gas expands against zero external pressure (vacuum)?
ⓐ. Maximum work is done
ⓑ. Minimum work is done
ⓒ. No work is done
ⓓ. Infinite work is done
Correct Answer: No work is done
Explanation: When a gas expands freely into a vacuum, there is no opposing force (( P_{\text{ext}} = 0 )), so ( w = -P_{\text{ext}} \Delta V = 0 ). This process, known as free expansion, involves no work transfer. Although the gas expands, no energy is used to move a boundary against resistance. Such processes are irreversible and are often used for conceptual understanding.
75. When work is done on the system by the surroundings, its sign according to the chemistry convention is:
ⓐ. Positive
ⓑ. Negative
ⓒ. Zero
ⓓ. Undefined
Correct Answer: Positive
Explanation: In chemistry, work done on the system (such as during compression) is taken as positive because the system gains energy. Conversely, work done by the system (such as during expansion) is negative because the system loses energy. This convention helps relate work and heat consistently in the first law ( \Delta U = q + w ).
76. Which of the following conditions results in maximum work done by a gas?
ⓐ. Expansion against constant external pressure
ⓑ. Free expansion into a vacuum
ⓒ. Reversible expansion
ⓓ. Isothermal compression
Correct Answer: Reversible expansion
Explanation: Maximum work is obtained in a reversible process because the system remains infinitesimally close to equilibrium throughout. In reversible expansion, external pressure changes gradually to match internal pressure, allowing continuous infinitesimal work. Any irreversible process, like free expansion, performs less work because of unbalanced forces and non-equilibrium conditions.
77. What type of work is associated with the expansion of a gas?
ⓐ. Electrical work
ⓑ. Chemical work
ⓒ. Pressure–volume work
ⓓ. Gravitational work
Correct Answer: Pressure–volume work
Explanation: Expansion or compression of gases involves pressure–volume (P–V) work. It occurs when the system’s volume changes under pressure. The equation ( w = -P_{\text{ext}} \Delta V ) describes this type of work. Other forms such as electrical work or surface work exist in different systems, but in gases, P–V work dominates energy changes.
78. In an isothermal reversible expansion of an ideal gas, the expression for work is:
ⓐ. ( w = nR(T_2 – T_1) )
ⓑ. ( w = -P_{\text{ext}} \Delta V )
ⓒ. ( w = -nRT \ln{\frac{V_2}{V_1}} )
ⓓ. ( w = 0 )
Correct Answer: ( w = -nRT \ln{\frac{V_2}{V_1}} )
Explanation: For a reversible isothermal expansion of an ideal gas, ( PV = nRT ) applies at all stages. Substituting into the integral ( w = -\int P,dV ) gives ( w = -nRT \ln(V_2/V_1) ). The work depends on temperature and the ratio of final to initial volumes. The process is slow and maintains thermal equilibrium throughout.
79. Which of the following statements correctly describes work in thermodynamics?
ⓐ. Work depends only on the initial and final states
ⓑ. Work depends on the path followed between two states
ⓒ. Work is a state function
ⓓ. Work is independent of the process type
Correct Answer: Work depends on the path followed between two states
Explanation: Work is a path function because its value varies with the process path taken between initial and final states. For instance, the work done during reversible expansion differs from that of irreversible expansion even if both have the same starting and ending pressures and volumes. In contrast, internal energy and enthalpy are state functions.
80. During the compression of a gas in a closed cylinder, which of the following statements is true?
ⓐ. Work is done by the system and internal energy decreases
ⓑ. Work is done on the system and internal energy increases
ⓒ. Work is zero and internal energy remains constant
ⓓ. Work is positive but internal energy decreases
Correct Answer: Work is done on the system and internal energy increases
Explanation: When gas is compressed, the surroundings apply force on the piston, doing work on the gas. According to ( \Delta U = q + w ), since ( w ) is positive, internal energy increases. The gas molecules move closer, increasing pressure and temperature. Such processes show how mechanical work influences energy changes inside a closed system.
81. What does the term pressure–volume (P–V) work represent in thermodynamics?
ⓐ. Work associated with change in temperature
ⓑ. Work due to electrical energy flow
ⓒ. Work done when the volume of a system changes against an external pressure
ⓓ. Work done during a chemical reaction only
Correct Answer: Work done when the volume of a system changes against an external pressure
Explanation: Pressure–volume work occurs when a system expands or compresses under an external pressure. The system performs work on the surroundings during expansion and vice versa during compression. The formula ( w = -P_{\text{ext}} \Delta V ) quantifies this work, where the negative sign shows that expansion causes energy loss from the system.
82. What is the correct mathematical expression for pressure–volume work done by a gas at constant external pressure?
ⓐ. ( w = P_{\text{ext}} \times V )
ⓑ. ( w = -P_{\text{ext}} \Delta V )
ⓒ. ( w = nRT \ln(V_2/V_1) )
ⓓ. ( w = q + \Delta U )
Correct Answer: ( w = -P_{\text{ext}} \Delta V )
Explanation: When a gas expands against a constant external pressure, the work done is given by ( w = -P_{\text{ext}} (V_2 – V_1) ). A positive ( \Delta V ) (expansion) gives negative work because the system loses energy, while a negative ( \Delta V ) (compression) gives positive work as the system gains energy. This relationship applies to irreversible processes at constant external pressure.
83. In the equation ( w = -P_{\text{ext}} \Delta V ), a negative value of ( w ) indicates that:
ⓐ. Work is done on the system
ⓑ. Heat is absorbed by the system
ⓒ. No work is done
ⓓ. Work is done by the system
Correct Answer: Work is done by the system
Explanation: A negative value of ( w ) arises when the system expands (( \Delta V > 0 )), meaning energy leaves the system as work done on the surroundings. Conversely, during compression (( \Delta V < 0 )), ( w ) becomes positive, indicating work done on the system. The sign convention helps track energy transfer direction in thermodynamic calculations.
84. A gas expands from 4.0 L to 10.0 L against a constant external pressure of 2.0 atm. What is the work done by the gas?
ⓐ. 12 L·atm
ⓑ. –12 L·atm
ⓒ. 8 L·atm
ⓓ. –8 L·atm
Correct Answer: –12 L·atm
Explanation: Using ( w = -P_{\text{ext}} \Delta V ),
( \Delta V = 10 – 4 = 6 , \text{L} ),
so ( w = -2.0 \times 6 = -12 , \text{L·atm} ).
The negative sign shows that work is done by the system. Converting to joules gives ( -12 \times 101.3 = -1216 , \text{J} ). Expansion always corresponds to energy loss by the system in the form of work.
85. For a gas compressed from 8.0 L to 3.0 L against an external pressure of 1.5 atm, what is the sign of work and its magnitude?
ⓐ. +7.5 L·atm
ⓑ. –7.5 L·atm
ⓒ. +5.0 L·atm
ⓓ. –5.0 L·atm
Correct Answer: +7.5 L·atm
Explanation: ( \Delta V = 3 – 8 = -5 , \text{L} ).
So ( w = -P_{\text{ext}} \Delta V = -1.5 \times (-5) = +7.5 , \text{L·atm} ).
The positive sign indicates that work is done on the system by the surroundings. In compression, the external agent applies force, increasing the system’s internal energy.
86. Which of the following conditions leads to zero pressure–volume work?
ⓐ. Isothermal expansion
ⓑ. Adiabatic compression
ⓒ. Constant volume process
ⓓ. Constant pressure process
Correct Answer: Constant volume process
Explanation: In a constant volume process, ( \Delta V = 0 ), so ( w = -P_{\text{ext}} \Delta V = 0 ). No boundary movement occurs, meaning no mechanical work is done. Energy may still transfer as heat, but P–V work specifically depends on volume change, so it is zero if volume remains constant.
87. When a gas expands reversibly and isothermally, the work done can be expressed as:
ⓐ. ( w = -nRT \ln(V_2/V_1) )
ⓑ. ( w = -P_{\text{ext}} \Delta V )
ⓒ. ( w = -C_p \Delta T )
ⓓ. ( w = -P\Delta V^2 )
Correct Answer: ( w = -nRT \ln(V_2/V_1) )
Explanation: In a reversible isothermal process, ( PV = nRT ) holds at every stage. Substituting ( P = nRT/V ) into ( w = -\int P,dV ) and integrating gives ( w = -nRT \ln(V_2/V_1) ). This represents the maximum possible work because the process occurs infinitely slowly, maintaining equilibrium throughout.
88. The unit of pressure–volume work when expressed in SI units is:
ⓐ. L·atm
ⓑ. Calorie
ⓒ. Joule
ⓓ. Erg
Correct Answer: Joule
Explanation: The SI unit of work is the joule (J). ( 1 , \text{L·atm} = 101.3 , \text{J} ). Work involves force multiplied by distance, both of which have SI units (newton and meter). In thermodynamics, work from volume–pressure relations is therefore converted from L·atm to joules for consistency with other energy quantities.
89. During expansion, a gas performs 300 J of work against constant external pressure. What happens to the system’s internal energy if no heat is supplied?
ⓐ. It increases by 300 J
ⓑ. It decreases by 300 J
ⓒ. It remains unchanged
ⓓ. It doubles
Correct Answer: It decreases by 300 J
Explanation: According to the first law ( \Delta U = q + w ). Here, ( q = 0 ) and ( w = -300 , \text{J} ) (work done by system). Thus, ( \Delta U = -300 , \text{J} ). The system loses internal energy because it does work without receiving heat from surroundings. The gas molecules move apart, lowering average kinetic energy.
90. Which of the following statements about P–V work is true?
ⓐ. It occurs only in solid systems
ⓑ. It occurs whenever a system changes its volume against external pressure
ⓒ. It can occur even when there is no volume change
ⓓ. It is independent of external pressure
Correct Answer: It occurs whenever a system changes its volume against external pressure
Explanation: P–V work arises whenever the system boundary moves due to a pressure difference. The magnitude depends on both external pressure and volume change. If external pressure equals zero or the volume is constant, no work is done. Hence, expansion or compression processes are the primary examples where pressure–volume work plays a role.
91. In thermodynamics, what is meant by heat?
ⓐ. Energy contained within a system
ⓑ. Energy transferred between system and surroundings because of a temperature difference
ⓒ. Energy stored in chemical bonds
ⓓ. Energy required to move a piston
Correct Answer: Energy transferred between system and surroundings because of a temperature difference
Explanation: Heat is not a property stored in a system but a form of energy transfer that occurs only when there is a temperature difference. When two bodies at different temperatures come into contact, energy flows from the hotter to the colder body until equilibrium is reached. Once equilibrium is achieved, there is no net heat flow.
92. Which of the following statements correctly describes heat transfer?
ⓐ. It occurs only when work is done
ⓑ. It flows from a colder to a hotter body spontaneously
ⓒ. It flows from a hotter to a colder body spontaneously
ⓓ. It depends only on pressure difference
Correct Answer: It flows from a hotter to a colder body spontaneously
Explanation: According to the second law of thermodynamics, heat transfer occurs naturally from higher to lower temperature until both reach equilibrium. To reverse this direction, external work must be done, as in refrigerators. Thus, temperature difference is the driving force for spontaneous heat flow, not pressure or volume difference.
93. Which of the following is true about heat and work?
ⓐ. Both are state functions
ⓑ. Both are path functions
ⓒ. Heat is a state function while work is not
ⓓ. Work is a state function while heat is not
Correct Answer: Both are path functions
Explanation: Heat and work depend on the process or path taken between two states. Their values change depending on how the process occurs, such as reversible or irreversible expansion. However, the total internal energy change (ΔU) depends only on initial and final states, making it a state function. Therefore, q and w are path functions, not state functions.
94. The SI unit of heat energy is:
ⓐ. Calorie
ⓑ. Erg
ⓒ. Joule
ⓓ. Electronvolt
Correct Answer: Joule
Explanation: The joule (J) is the SI unit of energy, including heat. Historically, calories were used to measure heat (1 cal = 4.184 J). Since the joule is derived from the mechanical definition of work (1 J = 1 N·m), it provides consistency with other forms of energy in thermodynamics. Thus, heat and work are both expressed in joules.
95. When a system absorbs heat, the sign of q according to chemistry convention is:
ⓐ. Positive
ⓑ. Negative
ⓒ. Zero
ⓓ. Undefined
Correct Answer: Positive
Explanation: In chemistry, the heat absorbed by a system is taken as positive because it increases the system’s internal energy. Conversely, when the system releases heat to surroundings, q is negative. This sign convention aligns with the first law of thermodynamics: ( \Delta U = q + w ), ensuring consistent tracking of energy flow direction.
96. Which of the following processes involves heat transfer but no work done?
ⓐ. Gas expansion in a piston
ⓑ. Boiling of water at constant pressure
ⓒ. Heating of water in an open vessel
ⓓ. Compression of gas in a cylinder
Correct Answer: Heating of water in an open vessel
Explanation: In an open vessel, heat flows into the water from the flame, increasing its temperature, but the vessel’s volume remains constant, so no mechanical work occurs. The energy transfer is purely as heat. In other cases like gas expansion or compression, both heat and work interactions take place simultaneously.
97. What happens during heat transfer between a system and surroundings?
ⓐ. Internal energy of the system always increases
ⓑ. Heat flows only into the system
ⓒ. Energy flows because of temperature difference
ⓓ. No energy is exchanged
Correct Answer: Energy flows because of temperature difference
Explanation: Heat flow is driven by the temperature gradient between system and surroundings. If the system is hotter, heat flows out; if cooler, heat flows in. The process continues until thermal equilibrium is reached. This exchange affects the internal energy of the system depending on whether it absorbs or loses heat.
98. Which device operates based primarily on heat transfer between two bodies?
ⓐ. Electric motor
ⓑ. Battery
ⓒ. Generator
ⓓ. Refrigerator
Correct Answer: Refrigerator
Explanation: A refrigerator transfers heat from a colder region (inside compartment) to a hotter region (outside atmosphere) using mechanical work. It operates on the reverse of natural heat flow, achieved by compressing and expanding a refrigerant fluid. Thus, refrigerators and heat pumps are practical examples of heat transfer control.
99. When a hot metal rod is placed in cold water, heat transfer continues until:
ⓐ. The rod and water reach the same temperature
ⓑ. All heat energy disappears
ⓒ. Water becomes colder than the rod
ⓓ. The rod stops releasing heat suddenly
Correct Answer: The rod and water reach the same temperature
Explanation: Heat energy always flows from a higher to a lower temperature body until thermal equilibrium is achieved. At this point, there is no net energy exchange, and both the metal rod and water attain the same temperature. This principle underlies calorimetry experiments where heat lost by one body equals heat gained by another.
100. In the first law of thermodynamics, the term q represents:
ⓐ. Work done by the system
ⓑ. Heat transferred between system and surroundings
ⓒ. Energy stored in chemical bonds
ⓓ. Change in entropy
Correct Answer: Heat transferred between system and surroundings
Explanation: In the equation ( \Delta U = q + w ), ( q ) denotes the heat absorbed or released by the system. If ( q > 0 ), heat flows into the system; if ( q < 0 ), heat flows out. It measures the thermal mode of energy transfer, distinguishing it from work, which involves mechanical or other non-thermal energy exchanges.
Welcome to Class 11 Chemistry MCQs – Chapter 6: Thermodynamics (Part of 4). If terms like ΔU, ΔH, ΔS, ΔG feel overwhelming, breathe—every topper once felt the same. This page is designed to make Thermodynamics feel friendly, doable, and score-boosting with 100 exam-focused MCQs and simple steps you can follow today.
Navigation & parts: The chapter has 395 MCQs in 4 parts (100 + 100 + 100 + 95). This page shows 100 MCQs with explanations. Use the Part buttons above (and page numbers, if visible) to continue smoothly.
What you will learn & practice (Chapter 6: Thermodynamics)
- System & surroundings; open/closed/isolated systems; intensive vs extensive properties
- State functions vs path functions; isothermal, isobaric, isochoric, adiabatic; reversible vs irreversible
- First Law of Thermodynamics: internal energy (ΔU), work (w), heat (q), enthalpy (ΔH)
- Heat capacity (C, Cp, Cv), relation for ideal gases, calorimetry numericals
- Hess’s Law, enthalpy of formation/combustion/solution/neutralization, phase changes
- Bond enthalpy, lattice enthalpy (idea), energy cycles & problem-solving
- Second Law & Entropy (ΔS): spontaneity idea, qualitative & quantitative questions
- Gibbs free energy (ΔG = ΔH − TΔS): feasibility and temperature effects
- Units, sign conventions, and quick exam shortcuts used often in Boards/JEE/NEET
How to use this site to master Thermodynamics MCQs
- Warm-up (10 mins): Keep a small formula sheet ready (ΔU, ΔH, ΔS, ΔG, Cp−Cv). Skim the topic list above.
- Active attempt: Solve 10–20 MCQs at a time. Click your option to get instant correct/incorrect feedback with a short explanation.
- Build your personal deck: Use the Heart on the right of any question to mark it as a Favourite (the heart turns red and the MCQ is added to your favourite list). Turn on the Favourite Toggle (just above the MCQs, to the right of the Random button) to see only your favourites for quick revision.
- Write it your way: Under each MCQ, click note button to note shortcuts, “why I got this wrong,” or neat tricks. Your notes auto-save and stay safe—they won’t be deleted—so you can return anytime and continue learning from your own words.
- Shuffle & strengthen: Use Random to shuffle questions. This prevents pattern memory and trains true understanding.
- Smart revision plan: Revisit your Favourite list on Day 2, Day 4, and Day 7 (spaced repetition). Before an exam, turn on Favourite Toggle and skim your Workspace notes—fast, focused revision without panic.
Why this helps for Boards, JEE Main & NEET
- Boards: Clear definitions + correct sign conventions = easy one-markers.
- JEE: Numericals on q, w, ΔU, ΔH and ΔG logic repeat often—practice builds speed.
- NEET: Conceptual questions on spontaneity, entropy trends, and enthalpy changes reward clarity over rote.
- Your edge: Favourite + Workspace turns messy chapters into a neat personal revision set.
Common mistakes to avoid
- Mixing up system vs surroundings and sign of q/w
- Forgetting ΔH ≠ ΔU when gas moles change (ideal gas)
- Treating q or w as state functions (they’re path functions)
- Unit slips: J vs kJ, Kelvin for temperature, consistent R value
- Ignoring temperature in ΔG = ΔH − TΔS while judging spontaneity
You’re not alone on this page—think of it as a quiet study room where every question teaches you one small lesson. Tag the good ones with ❤️, write your own Workspace hints, and come back once more. Progress will show.
Explore more: Class 11 Chemistry – Chapter Index, Class 11 – Subject Index, All Classes – MCQ Library.
Quick FAQ
Is Thermodynamics really tough?
It feels tough until signs and units are crystal clear. Do small sets of MCQs, mark favourites, and keep short Workspace notes—difficulty drops fast.
How many MCQs per day should I do?
Start with 30–40 daily. If time is short, do 20 focused MCQs and revise only your Favourite list.
What should I do a day before the exam?
Turn on the Favourite Toggle and revise only favourites + your Workspace notes. Fast, confident, and calm.
- 👉 Total MCQs in this chapter: 395 (100 + 100 + 100 + 95)
- 👉 This page: First 100 MCQs with answers & explanations
- 👉 Best for: Boards • JEE/NEET • Thermodynamics numericals • concept revision • quick quizzes
- 👉 Next: Use the Part buttons and page numbers above to continue
FAQs on Thermodynamics ▼
▸ What are Thermodynamics MCQs in Class 11 Chemistry?
These are multiple-choice questions from Chapter 6 of NCERT Class 11 Chemistry – Thermodynamics. They test your understanding of system and surroundings, state functions, work and heat, and energy changes in chemical processes.
▸ How many MCQs are available in this chapter?
There are a total of 395 Thermodynamics MCQs. They are divided into 4 structured parts – three sets of 100 questions each and one set of 95 questions.
▸ Are Thermodynamics MCQs important for JEE and NEET?
Yes, this chapter is highly important for JEE and NEET. Frequently tested areas include the First Law of Thermodynamics, enthalpy (ΔH), entropy (ΔS), Gibbs free energy (ΔG), spontaneity, Hess’s law, and calorimetry.
▸ Do these MCQs include correct answers and explanations?
Yes, every MCQ is provided with the correct answer and clear explanations to help you understand the reasoning and avoid rote learning.
▸ Which subtopics are covered in these Thermodynamics MCQs?
Subtopics include system and surroundings, intensive and extensive properties, state functions (U, H, S, G), work, heat and PV work, First Law, enthalpy changes, heat capacity (Cp, Cv), Hess’s law, bond enthalpy, entropy, Gibbs energy, spontaneity, and standard enthalpy of formation and combustion.