1. Which statement best describes the main focus of chemical kinetics?
ⓐ. It studies reaction rate and factors affecting it.
ⓑ. It studies only the heat change associated with a reaction.
ⓒ. It studies only the equilibrium composition of a reaction mixture.
ⓓ. It studies whether products are more stable than reactants, without considering time.
Correct Answer: It studies reaction rate and factors affecting it.
Explanation: Chemical kinetics is concerned with reaction rate, that is, how fast reactants are converted into products. It also examines how factors such as concentration, temperature, and catalysts influence that speed. Questions about heat evolved or final equilibrium composition belong to other aspects of chemistry, not the central purpose of kinetics.
2. Two reactions are both thermodynamically feasible. Which statement can still be true?
ⓐ. Both must occur at the same speed.
ⓑ. One may be fast while the other is very slow.
ⓒ. Neither can occur unless a catalyst is present.
ⓓ. Both must produce the same amount of heat.
Correct Answer: One may be fast while the other is very slow.
Explanation: Thermodynamic feasibility tells whether a reaction can occur, not how rapidly it proceeds. Chemical kinetics deals with the time aspect of the process. Therefore, two feasible reactions can differ greatly in rate because speed depends on kinetic factors, not feasibility alone.
3. Which question is answered primarily by chemical kinetics?
ⓐ. What is the value of the equilibrium constant?
ⓑ. Is the reaction exothermic or endothermic?
ⓒ. How quickly does a reactant concentration fall?
ⓓ. Is the product more stable than the reactant?
Correct Answer: How quickly does a reactant concentration fall?
Explanation: Chemical kinetics deals with the rate of reaction and with concentration changes as time passes. Questions about heat change are thermodynamic, and questions about stability or equilibrium constants are not direct rate questions. A time-based concentration change is a kinetic quantity.
4. A reaction is highly exothermic, but it proceeds very slowly at room temperature. This observation shows that
ⓐ. exothermic reactions must be non-spontaneous.
ⓑ. the reaction cannot form products at all.
ⓒ. heat released by a reaction directly fixes its speed.
ⓓ. reaction speed and energetic favourability differ.
Correct Answer: reaction speed and energetic favourability differ.
Explanation: A reaction may release a large amount of energy and still proceed slowly if the kinetic barrier is significant. Chemical kinetics describes how fast a reaction occurs, whereas energetic favourability concerns whether the process is thermodynamically allowed. The two ideas are related to different questions.
5. Which pair is matched correctly?
ⓐ. Thermodynamics — studies rate of reaction; Kinetics — studies heat of reaction
ⓑ. Thermodynamics — studies catalyst action only; Kinetics — studies equilibrium only
ⓒ. Thermodynamics — studies feasibility; Kinetics — studies speed
ⓓ. Thermodynamics — studies molecularity; Kinetics — studies spontaneity
Correct Answer: Thermodynamics — studies feasibility; Kinetics — studies speed
Explanation: Thermodynamics tells whether a process is energetically possible or favourable. Chemical kinetics tells how fast that process takes place. This distinction is fundamental because a feasible reaction may still be very slow.
6. Rusting of iron often takes place over a long period, whereas ionic precipitation can occur almost immediately. The most appropriate conclusion is that
ⓐ. both processes must have the same reaction rate because both form products.
ⓑ. only slow reactions can occur naturally.
ⓒ. visible product formation always means the reaction is fast.
ⓓ. chemical reactions can differ widely in the time they take to proceed.
Correct Answer: chemical reactions can differ widely in the time they take to proceed.
Explanation: Some reactions are nearly instantaneous, while others require hours, days, or longer. This wide variation in time of occurrence is one of the central reasons for studying chemical kinetics. The presence of products does not imply equal reaction speeds.
7. Which statement is correct for the study of reaction progress in chemical kinetics?
ⓐ. It follows conversion of reactants into products with time.
ⓑ. It ignores time and compares only initial and final states.
ⓒ. It applies only after equilibrium has been reached.
ⓓ. It applies only to reactions involving gases.
Correct Answer: It follows conversion of reactants into products with time.
Explanation: Chemical kinetics follows the progress of a reaction with time. The core idea is that the composition of the reacting system changes as reactants are consumed and products are formed. Time is therefore an essential variable in kinetic study.
8. Which statement best distinguishes a kinetic description from a thermodynamic description?
ⓐ. A kinetic description states whether the reaction mixture contains solids or liquids.
ⓑ. A kinetic description tells whether the reaction equation is balanced.
ⓒ. A kinetic description tells how fast the system moves toward products.
ⓓ. A kinetic description tells only the total mass of products formed.
Correct Answer: A kinetic description tells how fast the system moves toward products.
Explanation: Kinetics is the time-dependent description of a reaction. It focuses on the speed of conversion of reactants into products and how that speed changes. A thermodynamic description, in contrast, addresses feasibility, stability, or energy aspects rather than reaction speed.
9. Two samples of different reactions are both capable of forming products under suitable conditions. One shows a visible change in seconds, while the other changes only after several hours. This difference is mainly a matter of
ⓐ. equilibrium position.
ⓑ. reaction rate.
ⓒ. molecular formula.
ⓓ. stoichiometric ratio.
Correct Answer: reaction rate.
Explanation: The key difference here is the time taken for observable chemical change. Chemical kinetics deals with how fast a reaction proceeds, so reactions that occur in seconds and reactions that take hours differ mainly in rate.
10. Which observation is least useful when the aim is to study how fast a reaction proceeds?
ⓐ. Time taken for turbidity to appear
ⓑ. Concentration of a reactant at regular intervals
ⓒ. Volume of gas evolved with time
ⓓ. Standard enthalpy change of the reaction
Correct Answer: Standard enthalpy change of the reaction
Explanation: Rate study requires a measurable change with time, such as concentration, gas volume, or appearance of turbidity. Standard enthalpy change describes the heat effect of the reaction, not the speed at which the reaction occurs.
11. Which statement is not necessarily true for a chemically feasible reaction?
ⓐ. It must occur rapidly at ordinary conditions.
ⓑ. It may proceed slowly because of a kinetic barrier.
ⓒ. It can take a long time to show noticeable change.
ⓓ. Its speed must be considered separately from feasibility.
Correct Answer: It must occur rapidly at ordinary conditions.
Explanation: Feasibility and speed are different ideas. A reaction may be capable of occurring and yet proceed very slowly under ordinary conditions. That is why reaction rate has to be studied separately.
12. Which quantity is commonly used to express how fast a chemical reaction is taking place?
ⓐ. Change in colour of the vessel with time
ⓑ. Change in molar mass of the catalyst with time
ⓒ. Concentration change with time
ⓓ. Change in atomic number of an element with time
Correct Answer: Concentration change with time
Explanation: Reaction rate is measured through how the concentration of reactants decreases or how the concentration of products increases as time passes. Concentration-time data therefore provide a direct way to describe reaction speed.
13. Why must a time interval be specified when describing how fast a reaction proceeds?
ⓐ. Because time fixes the stoichiometric coefficients of the reaction
ⓑ. Because time determines the equilibrium constant directly
ⓒ. Because time changes the chemical formula of the reactants
ⓓ. Because rate uses concentration change over a time interval
Correct Answer: Because rate uses concentration change over a time interval
Explanation: A reaction rate has meaning only when the concentration change is connected to a particular interval of time. Without the time interval, the amount of change alone does not tell how fast the reaction occurred.
14. For the same reaction, measured values of rate may differ when different observation intervals are chosen because
ⓐ. concentration has no role in deciding rate.
ⓑ. the interval changes the measured rate.
ⓒ. the balanced equation changes with time.
ⓓ. the product stops obeying stoichiometry.
Correct Answer: the interval changes the measured rate.
Explanation: The observed rate depends on how much concentration changes during the interval being considered. If the interval changes, the measured concentration change per unit time can also change, especially as the reaction progresses.
15. Which set of data is most suitable for following the progress of a reaction with time?
ⓐ. Initial colour of the mixture only
ⓑ. Final temperature of the mixture only
ⓒ. Reactant concentration at known times
ⓓ. Melting point of the isolated product only
Correct Answer: Reactant concentration at known times
Explanation: To track reaction progress, one needs repeated measurements linked to time. A series of concentration values taken at known times shows how the reacting system changes as the reaction proceeds.
16. For the reaction \(A \rightarrow B\), which observation clearly indicates forward reaction progress?
ⓐ. \([A]\) decreases while \([B]\) increases with time
ⓑ. \([A]\) and \([B]\) remain unchanged from the start
ⓒ. \([A]\) increases while \([B]\) decreases in a closed system
ⓓ. The mass number of \(A\) decreases with time
Correct Answer: \([A]\) decreases while \([B]\) increases with time
Explanation: In forward progress, reactant particles are consumed and product particles are formed. Therefore the concentration of \(A\) falls while the concentration of \(B\) rises as time passes.
17. A student says, “The reaction rate is 0.20.” Which additional information is essential before this statement becomes meaningful?
ⓐ. The colour of the reaction mixture
ⓑ. The concentration change and time interval
ⓒ. The balanced equation written in ionic form
ⓓ. The molar mass of each reactant
Correct Answer: The concentration change and time interval
Explanation: A reaction rate is defined through how much concentration changes in a given time. A number alone is incomplete unless it is tied to a concentration change per unit time. That is why both concentration information and the corresponding time interval are necessary.
18. Which quantity can directly serve as a measurable basis for reaction rate?
ⓐ. Change in concentration with time
ⓑ. Number of atoms in one molecule
ⓒ. Valency of the product element
ⓓ. Standard atomic mass of the reactant
Correct Answer: Change in concentration with time
Explanation: Reaction rate is measured from how quickly the concentration of a reactant decreases or that of a product increases. Atomic mass, valency, and atom count do not by themselves tell how fast a reaction is proceeding.
19. In a reaction mixture, the concentration of a reactant falls rapidly during the first few seconds and then decreases more slowly later. This shows that
ⓐ. the reaction rate must remain constant throughout.
ⓑ. the reaction has stopped after the first few seconds.
ⓒ. only products determine the rate of reaction.
ⓓ. the rate can change as the reaction proceeds.
Correct Answer: the rate can change as the reaction proceeds.
Explanation: Rate is often larger at the beginning and smaller later because the concentrations of reactants usually decrease with time. As the reaction progresses, the concentration-time pattern can change, so the rate need not stay constant.
20. Which statement correctly explains why concentration is commonly used to express reaction rate?
ⓐ. Concentration can show how composition changes with time.
ⓑ. Concentration remains the same throughout a reaction.
ⓒ. Concentration gives the activation energy directly.
ⓓ. Concentration is independent of the amount of substance present.
Correct Answer: Concentration can show how composition changes with time.
Explanation: The progress of a reaction is reflected in changing amounts of reactants and products. Expressing these changes through concentration makes it possible to connect composition with time, which is exactly what rate measurement requires.
