1. Thermodynamics mainly deals with the study of changes involving heat, work, energy, and matter. In chemistry, its use is most directly seen when we study
ⓐ. only the colour of substances before and after reaction
ⓑ. only the names of reactants and products
ⓒ. only the shape of laboratory glassware
ⓓ. energy changes in physical and chemical processes
Correct Answer: energy changes in physical and chemical processes
Explanation: Thermodynamics studies energy changes and energy transfer during processes. In chemistry, this includes heat evolved or absorbed during reactions, work associated with expansion or compression, and energy changes during physical changes such as melting or vaporization. It does not depend only on visible colour change or on naming substances. A reaction may show no obvious colour change but may still involve a large energy change. The central idea is to account for energy in a process, not merely to describe what the substances look like.
2. A piece of ice melts slowly in a beaker at room temperature. The thermodynamic aspect of this observation is mainly connected with
ⓐ. change in the atomic number of oxygen
ⓑ. heat transfer between ice and surroundings
ⓒ. formation of a new element from hydrogen
ⓓ. conversion of mass completely into electrical charge
Correct Answer: heat transfer between ice and surroundings
Explanation: Melting is a physical change involving heat transfer from the surroundings to the ice. The chemical identity of water remains the same during melting, so no new element or change in atomic number is involved. Thermodynamics can study this process because energy is exchanged even though no chemical reaction occurs. The process shows that thermodynamics applies to both physical and chemical changes. The useful point here is that an energy change may occur even when the substance remains chemically the same.
3. Burning of \(\mathrm{CH_4}\) in oxygen is an important thermodynamic example because it
ⓐ. occurs without any energy change
ⓑ. changes carbon atoms into oxygen atoms
ⓒ. produces heat along with chemical products
ⓓ. proves that temperature and heat are identical quantities
Correct Answer: produces heat along with chemical products
Explanation: Combustion of methane is a chemical reaction that releases energy as heat. Thermodynamics studies this energy release along with the relation between reactants and products. The atoms are rearranged during the reaction; carbon atoms do not become oxygen atoms. Temperature and heat are related but not identical, because temperature describes hotness while heat is energy transferred due to temperature difference. Combustion is a good early example because it connects a chemical change with a measurable energy effect.
4. The SI unit of energy used in thermodynamics is
ⓐ. \(\mathrm{J}\)
ⓑ. \(\mathrm{mol}\)
ⓒ. \(\mathrm{K}\)
ⓓ. \(\mathrm{Pa}\)
Correct Answer: \(\mathrm{J}\)
Explanation: The joule, written as \(\mathrm{J}\), is the SI unit of energy. Heat and work are both modes of energy transfer, so they are also measured in \(\mathrm{J}\). The unit \(\mathrm{mol}\) measures amount of substance, \(\mathrm{K}\) measures temperature, and \(\mathrm{Pa}\) measures pressure. Chemistry thermodynamics often uses \(\mathrm{kJ}\) because reaction energy changes may be large. Confusing \(\mathrm{J}\) with \(\mathrm{K}\) mixes energy with temperature, which are different physical quantities.
5. A hot metal spoon is placed in colder water. The statement that best describes the heat transfer is
ⓐ. heat is transferred from colder water to the hotter spoon
ⓑ. heat is transferred from the hotter spoon to colder water
ⓒ. temperature is transferred from the spoon to water
ⓓ. work is transferred because the spoon is metallic
Correct Answer: heat is transferred from the hotter spoon to colder water
Explanation: Heat is energy transferred because of a temperature difference. It flows from the body at higher temperature to the body at lower temperature until thermal balance is approached. Temperature itself is not a form of energy transferred from one body to another. The metallic nature of the spoon may affect how quickly heat is conducted, but the driving reason is the temperature difference. This separates the idea of heat transfer from the idea of temperature as a property of a body.
6. In a thermodynamics record, an energy change is written as \(5\,\text{kJ}\). This is equal to
ⓐ. \(5\,\text{J}\)
ⓑ. \(50\,\text{J}\)
ⓒ. \(5000\,\text{J}\)
ⓓ. \(500.0\,\text{J}\)
Correct Answer: \(5000\,\text{J}\)
Explanation: \( \textbf{Known relation:} \) \(1\,\text{kJ}=1000\,\text{J}\).
\( \textbf{Given quantity:} \) \(5\,\text{kJ}\).
\( \textbf{Conversion:} \)
\[
5\,\text{kJ}=5\times1000\,\text{J}
\]
\[
5\,\text{kJ}=5000\,\text{J}
\]
\( \textbf{Unit meaning:} \) The prefix \(\text{kilo}\) means \(1000\), not \(10\) or \(100\).
\( \textbf{Final answer:} \) \(5\,\text{kJ}=5000\,\text{J}\). Using \(\text{kJ}\) instead of \(\text{J}\) changes only the size of the unit, not the type of quantity.
7. A cup of tea cools on a table. From a thermodynamic point of view, the most suitable description is that
ⓐ. the surroundings lose heat to the hotter tea
ⓑ. the tea gains temperature from the air
ⓒ. the mass of tea must increase during cooling
ⓓ. the tea loses heat to its surroundings
Correct Answer: the tea loses heat to its surroundings
Explanation: A hot object cools because heat is transferred from the hotter object to cooler surroundings. The tea is initially at a higher temperature than the surrounding air, so the direction of heat flow is outward from the tea. Temperature is not a substance that is gained or lost; it is a measure related to the thermal state. The mass of the tea need not increase simply because it cools. Cooling is a basic thermodynamic process because it involves energy transfer without needing a chemical reaction.
8. The pair in which both quantities are forms of energy transfer in thermodynamics is
ⓐ. temperature and pressure
ⓑ. mole and volume
ⓒ. mass and density
ⓓ. heat and work
Correct Answer: heat and work
Explanation: Heat and work are two ways by which energy can be transferred between a system and its surroundings. Heat transfer occurs because of temperature difference, while work transfer is associated with organized force-displacement effects such as expansion or compression. Temperature and pressure describe the state of matter, but they are not themselves forms of energy transfer. Mole, volume, mass, and density are useful physical quantities, but they do not by themselves describe energy crossing a boundary. The distinction becomes important later when energy balance is written using heat and work terms.
9. The relation \(1\,\text{cal}=4.184\,\text{J}\) is used to express heat values in SI units. A heat value of \(10\,\text{cal}\) corresponds to
ⓐ. \(2.39\,\text{J}\)
ⓑ. \(41.84\,\text{J}\)
ⓒ. \(4.184\,\text{J}\)
ⓓ. \(418.4\,\text{J}\)
Correct Answer: \(41.84\,\text{J}\)
Explanation: \( \textbf{Given relation:} \) \(1\,\text{cal}=4.184\,\text{J}\).
\( \textbf{Given heat value:} \) \(10\,\text{cal}\).
\( \textbf{Substitution:} \)
\[
10\,\text{cal}=10\times4.184\,\text{J}
\]
\[
10\,\text{cal}=41.84\,\text{J}
\]
\( \textbf{Unit check:} \) The answer must be in \(\text{J}\) because the question asks for SI energy units.
\( \textbf{Final answer:} \) \(10\,\text{cal}=41.84\,\text{J}\). Multiplying by \(4.184\) is needed when converting from \(\text{cal}\) to \(\text{J}\).
10. A reaction vessel becomes warm to touch during a reaction. The simplest thermodynamic conclusion is that
ⓐ. the reaction has no energy change
ⓑ. the vessel has converted all reactants into temperature
ⓒ. there was heat transfer to the vessel and surroundings
ⓓ. the reaction must have stopped immediately
Correct Answer: there was heat transfer to the vessel and surroundings
Explanation: A warm vessel indicates that heat has been transferred from the reacting system to the vessel and nearby surroundings. This is a thermodynamic observation because it involves energy transfer during a chemical change. The reactants are not converted into temperature; temperature is a property that changes when energy is transferred. The reaction need not stop simply because heat is produced. The observation gives information about heat flow, but a complete thermodynamic calculation would require defined system, surroundings, and measured quantities.
11. In thermodynamics, the part of the universe chosen for study is called the
ⓐ. boundary
ⓑ. surroundings
ⓒ. reservoir
ⓓ. system
Correct Answer: system
Explanation: The system is the part of the universe selected for thermodynamic study. Everything outside the system is called the surroundings. The boundary separates the system from the surroundings and may be real or imaginary. A reservoir is a special large body that can supply or absorb heat without much temperature change, but it is not the general term for the chosen part. Identifying the system first is essential because heat and work signs are always described with respect to the system.
12. A reaction mixture in a flask is selected for thermodynamic study. The air, table, and room outside the flask are mainly part of the
ⓐ. system
ⓑ. chemical equation
ⓒ. surroundings
ⓓ. internal composition
Correct Answer: surroundings
Explanation: Once the reaction mixture is selected as the system, everything outside it is treated as the surroundings. The surroundings may include the flask wall, air, table, and the rest of the room depending on how the boundary is chosen. The chemical equation describes the reaction but is not a physical region outside the system. Internal composition belongs to the system, not to what lies outside it. This separation allows energy exchange to be described clearly between the system and surroundings.
13. The universe in a thermodynamic description is represented as
ⓐ. system plus surroundings
ⓑ. system only
ⓒ. surroundings only
ⓓ. boundary plus thermometer only
Correct Answer: system plus surroundings
Explanation: In thermodynamics, the universe means the system together with its surroundings. The boundary is the separating surface between them, not a separate third region that replaces either one. A thermometer may be used for measurement, but it is not part of the general definition of universe. The chosen system may be small, such as a gas in a cylinder, while the surroundings include everything outside it. This simple division is the starting point for discussing energy conservation.
14. A beaker contains an aqueous solution of \(\mathrm{NaCl}\), and only the solution is selected for study. The glass wall of the beaker is best described as
ⓐ. necessarily a part of the selected system
ⓑ. the whole thermodynamic universe
ⓒ. a boundary between system and surroundings
ⓓ. the chemical surroundings inside the solution
Correct Answer: a boundary between system and surroundings
Explanation: If only the solution is chosen as the system, the beaker wall can act as part of the boundary separating the solution from the outside. A boundary may be real, such as a wall, or imaginary, depending on how the system is defined. The beaker wall is not necessarily part of the system unless the observer chooses solution plus beaker as the system. It is also not the whole universe, because the universe includes both system and surroundings. The choice of system decides what is inside the boundary and what is outside it.
15. Match each thermodynamic term with its most suitable meaning.
| Term | Meaning |
|---|
| P. System | 1. Everything outside the chosen part |
| Q. Surroundings | 2. Chosen part under study |
| R. Boundary | 3. Separating surface between chosen part and outside |
| S. Universe | 4. System and surroundings together |
ⓐ. P-2, Q-1, R-3, S-4
ⓑ. P-1, Q-2, R-3, S-4
ⓒ. P-2, Q-3, R-1, S-4
ⓓ. P-4, Q-1, R-2, S-3
Correct Answer: P-2, Q-1, R-3, S-4
Explanation: The system is the chosen part under study, while the surroundings are everything outside that chosen part. The boundary separates the system from the surroundings and may be real or imaginary. The universe in thermodynamics is the combination of system and surroundings. A mapping that reverses system and surroundings changes the reference for heat and work descriptions. The terms must be fixed before applying sign conventions or energy balance.
16. A gas enclosed in a cylinder fitted with a piston is selected as the system. The piston surface in contact with the gas mainly represents
ⓐ. a reactant inside the gas
ⓑ. the whole surroundings
ⓒ. a thermodynamic property of the gas
ⓓ. a boundary of the system
Correct Answer: a boundary of the system
Explanation: The piston surface separates the gas chosen as the system from the outside region. Therefore, it acts as a boundary through which mechanical interaction may occur. The piston itself is not a reactant unless it chemically participates, which is not stated here. The surroundings include the external region beyond the gas, not only the piston surface. Recognising the piston as a boundary prepares the later idea that expansion or compression work can occur when the boundary moves.
17. A student writes the following description: “For a reaction mixture taken as system, the surroundings are only the chemicals not participating in the reaction.” The best evaluation of this claim is that
ⓐ. it is valid because surroundings always mean unreacted chemicals only
ⓑ. it is limited because surroundings include all outside matter
ⓒ. it is valid only when the reaction is exothermic
ⓓ. it is valid only when the reaction is carried out at \(298\,\text{K}\)
Correct Answer: it is limited because surroundings include all outside matter
Explanation: Surroundings are not restricted to unused or unreacted chemicals. Once the reaction mixture is chosen as the system, the surroundings include everything outside that chosen system, such as the container, air, and laboratory region as relevant to the description. Whether the reaction is exothermic or endothermic does not change the basic definition of surroundings. The temperature \(298\,\text{K}\) is a commonly used reference temperature in many thermodynamic discussions, but it is not part of the definition of surroundings. The system choice, not chemical participation alone, decides the system-surroundings separation.
18. Read the situation below and answer the question.
A small amount of water is heated in a test tube. For one thermodynamic description, only the water is chosen as the system.
What belongs to the surroundings in this description?
ⓐ. only the water molecules
ⓑ. matter outside the selected water
ⓒ. only the dissolved gases inside the water
ⓓ. the system and surroundings together
Correct Answer: matter outside the selected water
Explanation: The selected system is only the water, so objects and matter outside the water form the surroundings. The test tube, flame, and surrounding air may exchange energy with the water, so they lie outside the system in this description. Dissolved gases inside the selected water would normally be part of the system if they are included in the water sample. The phrase “system and surroundings together” describes the thermodynamic universe, not the surroundings alone. This example shows that system choice is a matter of definition before energy transfer is discussed.
19. The boundary of a thermodynamic system may be real or imaginary. An example of an imaginary boundary is best represented by
ⓐ. an imagined surface in the solution
ⓑ. the glass wall of a sealed bottle
ⓒ. the metal wall of a gas cylinder
ⓓ. the rigid wall of a steel container
Correct Answer: an imagined surface in the solution
Explanation: A boundary is the surface separating the system from its surroundings. It may be a real physical wall, such as glass or metal, or an imaginary surface chosen for analysis. A mentally drawn surface around part of a solution has no material wall, so it is an imaginary boundary. The glass bottle wall, gas cylinder wall, and steel container wall are real boundaries. Imaginary boundaries are useful because thermodynamics allows the system to be defined according to the process being studied.
20. Two descriptions are given for the same beaker containing a dissolving salt.
I. The system is only the salt crystals before they dissolve.
II. The system is the entire salt-water mixture during dissolving.
How does the surroundings description change?
ⓐ. It changes with the chosen system
ⓑ. It cannot change because surroundings are fixed for all choices
ⓒ. It changes only if the salt is coloured
ⓓ. It is always limited to the air above the beaker
Correct Answer: It changes with the chosen system
Explanation: The surroundings are defined relative to the selected system. If only the salt crystals are the system, then water and the rest of the beaker contents may be outside that system. If the whole salt-water mixture is selected as the system, the surroundings become the beaker, air, and other external parts. The colour of the salt does not decide system boundaries. Thermodynamic descriptions must state the chosen system clearly because changing the system changes what is counted as outside it.
