A reaction intermediate, unlike a transition state, is

A species that is formed and then consumed during the reaction mechanism, with a finite lifetime

A transition state (activated complex) is

A high-energy, unstable, transient arrangement of atoms during a reaction

The rate-determining step of a multi-step reaction mechanism is the

Slowest step, which controls the overall rate

Chemical Kinetics MCQs 2026

46 questions with detailed answers · 19 from past papers · 5 quiz batches available

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Page 1 of 1 Questions 1–10 of 46

Q1 medium

The units of a rate constant depend on the
1. A Overall order of the reaction
2. B Temperature only
3. C Volume of the container
4. D Nature of the catalyst
💡 Explanation:
Rate constant units vary systematically depending on the overall order of the reaction.
Q2 Past Paper · PPSC/FPSC/NTS medium

A reaction intermediate, unlike a transition state, is
1. A Never formed during a reaction
2. B The same as activation energy
3. C Always the final product
4. D A species that is formed and then consumed during the reaction mechanism, with a finite lifetime
💡 Explanation:
Reaction intermediates are actual, if short-lived, chemical species formed and consumed during the mechanism.
Q3 medium

Which of the following would increase the frequency of effective collisions between reactant molecules
1. A Increasing temperature
2. B Decreasing concentration
3. C Decreasing surface area
4. D Removing the catalyst
💡 Explanation:
Higher temperature increases molecular speed and energy, raising the frequency of effective collisions.
Q4 medium

A transition state (activated complex) is
1. A A high-energy, unstable, transient arrangement of atoms during a reaction
2. B A stable intermediate that can be isolated
3. C The same as a catalyst
4. D The final product of a reaction
💡 Explanation:
The transition state is a fleeting, high-energy configuration at the peak of the energy barrier.
Q5 Past Paper · PPSC/FPSC/NTS medium

The rate-determining step of a multi-step reaction mechanism is the
1. A Fastest step
2. B First step always
3. C Last step always
4. D Slowest step, which controls the overall rate
💡 Explanation:
The slowest step in a mechanism acts as a bottleneck, controlling the overall observed rate.
Q6 medium

Radioactive decay follows ___ order kinetics
1. A First
2. B Second
3. C Zero
4. D Third
💡 Explanation:
Radioactive decay is a classic example of a first-order kinetic process.
Q7 medium

The half-life of a first-order reaction is
1. A Independent of the initial concentration of reactant
2. B Directly proportional to initial concentration
3. C Inversely proportional to initial concentration
4. D Equal to zero
💡 Explanation:
A defining feature of first-order kinetics is that half-life remains constant regardless of starting concentration.
Q8 Past Paper · PPSC/FPSC/NTS medium

The Arrhenius equation relates the rate constant k to the
1. A Concentration of products
2. B Order of reaction only
3. C Equilibrium constant
4. D Temperature and activation energy
💡 Explanation:
The Arrhenius equation expresses k as a function of temperature and activation energy.
Q9 medium

The rate constant, k, of a reaction depends on
1. A Concentration of reactants only
2. B Volume of container
3. C Temperature (and the presence of a catalyst)
4. D Time elapsed
💡 Explanation:
The rate constant is affected by temperature and catalysts, but not by reactant concentration.
Q10 medium

The overall order of a reaction is the sum of the
1. A Coefficients in the balanced equation
2. B Molar masses of reactants
3. C Activation energies
4. D Exponents of concentration terms in the rate law
💡 Explanation:
Overall reaction order is found by adding together all the exponents in the experimentally determined rate law.
Q11 Past Paper · PPSC/FPSC/NTS medium

For a zero-order reaction, the rate is
1. A Independent of the concentration of reactant
2. B Directly proportional to concentration
3. C Proportional to the square of concentration
4. D Always equal to zero
💡 Explanation:
In a zero-order reaction, changing reactant concentration does not affect the rate.
Q12 medium

For a reaction with rate = k[A]^1, the reaction is said to be ___ order with respect to A
1. A First
2. B Second
3. C Zero
4. D Third
💡 Explanation:
An exponent of 1 on the concentration term indicates first-order dependence on that reactant.
Q13 Past Paper · PPSC/FPSC/NTS medium

The rate law of a reaction must be determined
1. A From the balanced chemical equation directly
2. B From thermodynamic data
3. C Experimentally
4. D From the equilibrium constant
💡 Explanation:
Rate laws cannot be predicted from stoichiometry alone; they must be found through experiment.
Q14 medium

According to collision theory, for a reaction to occur, reacting particles must collide with
1. A Any energy and any orientation
2. B Sufficient energy but any orientation is fine
3. C Correct orientation but energy is irrelevant
4. D Sufficient energy and proper orientation
💡 Explanation:
Collision theory requires both adequate energy and correct geometric orientation for a successful reaction.
Q15 easy

A reaction with a lower activation energy will generally proceed
1. A More slowly
2. B At the same rate as one with high Ea
3. C Not at all
4. D Faster
💡 Explanation:
Lower activation energy means more molecules have sufficient energy to react, speeding the reaction.
Q16 Past Paper · PPSC/FPSC/NTS easy

The activation energy of a reaction is
1. A The total energy released in the reaction
2. B The energy of the products
3. C Equal to the enthalpy change of the reaction
4. D The minimum energy required for reactants to form products
💡 Explanation:
Activation energy is the energy barrier that reacting particles must overcome to form products.
Q17 easy

Increasing the surface area of a solid reactant generally ___ the reaction rate
1. A Decreases
2. B Has no effect on
3. C Increases
4. D Reverses
💡 Explanation:
Greater surface area exposes more reactant particles to collisions, increasing reaction rate.
Q18 Past Paper · PPSC/FPSC/NTS easy

A catalyst is not consumed in a reaction; it is regenerated at the
1. A Beginning of the reaction only
2. B End of the reaction, remaining chemically unchanged
3. C Transition state only
4. D Rate-determining step only, then destroyed
💡 Explanation:
Catalysts participate in the mechanism but are fully regenerated, unchanged, by the reaction's end.
Q19 easy

A catalyst increases the rate of a reaction by
1. A Increasing the temperature of the system
2. B Increasing the concentration of reactants
3. C Lowering the activation energy of the reaction
4. D Shifting the equilibrium position
💡 Explanation:
Catalysts provide an alternate pathway with lower activation energy, speeding up the reaction.
Q20 Past Paper · PPSC/FPSC/NTS easy

Increasing the concentration of reactants generally ___ the rate of reaction
1. A Decreases
2. B Has no effect on
3. C Reverses
4. D Increases
💡 Explanation:
Higher reactant concentration increases collision frequency, generally increasing reaction rate.
Q21 easy

Increasing the temperature of a reaction generally ___ its rate
1. A Decreases
2. B Increases
3. C Has no effect on
4. D Reverses
💡 Explanation:
Higher temperature increases molecular energy and collision frequency, speeding up reactions.
Q22 Past Paper · PPSC/FPSC/NTS easy

Which of the following factors does NOT typically affect the rate of a reaction
1. A Temperature
2. B Concentration of reactants
3. C Presence of a catalyst
4. D Color of the container
💡 Explanation:
The container's color has no chemical influence on reaction rate, unlike temperature, concentration, and catalysts.
Q23 Past Paper · PPSC/FPSC/NTS easy

The rate of a chemical reaction is generally expressed as the change in concentration of reactant or product per unit
1. A Volume
2. B Time
3. C Mass
4. D Pressure
💡 Explanation:
Reaction rate is defined as the change in concentration divided by the elapsed time.
Q24 easy

Chemical kinetics is the study of the
1. A Position of equilibrium
2. B Heat changes in reactions
3. C Rate and mechanism of chemical reactions
4. D Structure of molecules
💡 Explanation:
Chemical kinetics examines how fast reactions occur and the steps by which they proceed.
Q25 easy

Increasing the temperature of a reaction generally ___ its rate
1. A Decreases
2. B Increases
3. C Has no effect on
4. D Reverses
💡 Explanation:
Higher temperature increases molecular energy and collision frequency, speeding up reactions.
Q26 Past Paper · PPSC/FPSC/NTS easy

Increasing the concentration of reactants generally ___ the rate of reaction
1. A Decreases
2. B Has no effect on
3. C Reverses
4. D Increases
💡 Explanation:
Higher reactant concentration increases collision frequency, generally increasing reaction rate.
Q27 easy

A catalyst increases the rate of a reaction by
1. A Increasing the temperature of the system
2. B Increasing the concentration of reactants
3. C Lowering the activation energy of the reaction
4. D Shifting the equilibrium position
💡 Explanation:
Catalysts provide an alternate pathway with lower activation energy, speeding up the reaction.
Q28 Past Paper · PPSC/FPSC/NTS easy

A catalyst is not consumed in a reaction; it is regenerated at the
1. A Beginning of the reaction only
2. B End of the reaction, remaining chemically unchanged
3. C Transition state only
4. D Rate-determining step only, then destroyed
💡 Explanation:
Catalysts participate in the mechanism but are fully regenerated, unchanged, by the reaction's end.
Q29 easy

Increasing the surface area of a solid reactant generally ___ the reaction rate
1. A Decreases
2. B Has no effect on
3. C Increases
4. D Reverses
💡 Explanation:
Greater surface area exposes more reactant particles to collisions, increasing reaction rate.
Q30 Past Paper · PPSC/FPSC/NTS easy

The activation energy of a reaction is
1. A The total energy released in the reaction
2. B The energy of the products
3. C Equal to the enthalpy change of the reaction
4. D The minimum energy required for reactants to form products
💡 Explanation:
Activation energy is the energy barrier that reacting particles must overcome to form products.
Q31 easy

A reaction with a lower activation energy will generally proceed
1. A More slowly
2. B At the same rate as one with high Ea
3. C Not at all
4. D Faster
💡 Explanation:
Lower activation energy means more molecules have sufficient energy to react, speeding the reaction.
Q32 medium

According to collision theory, for a reaction to occur, reacting particles must collide with
1. A Any energy and any orientation
2. B Sufficient energy but any orientation is fine
3. C Correct orientation but energy is irrelevant
4. D Sufficient energy and proper orientation
💡 Explanation:
Collision theory requires both adequate energy and correct geometric orientation for a successful reaction.
Q33 Past Paper · PPSC/FPSC/NTS medium

The rate law of a reaction must be determined
1. A From the balanced chemical equation directly
2. B From thermodynamic data
3. C Experimentally
4. D From the equilibrium constant
💡 Explanation:
Rate laws cannot be predicted from stoichiometry alone; they must be found through experiment.
Q34 medium

For a reaction with rate = k[A]^1, the reaction is said to be ___ order with respect to A
1. A First
2. B Second
3. C Zero
4. D Third
💡 Explanation:
An exponent of 1 on the concentration term indicates first-order dependence on that reactant.
Q35 Past Paper · PPSC/FPSC/NTS medium

For a zero-order reaction, the rate is
1. A Independent of the concentration of reactant
2. B Directly proportional to concentration
3. C Proportional to the square of concentration
4. D Always equal to zero
💡 Explanation:
In a zero-order reaction, changing reactant concentration does not affect the rate.
Q36 medium

The overall order of a reaction is the sum of the
1. A Coefficients in the balanced equation
2. B Molar masses of reactants
3. C Activation energies
4. D Exponents of concentration terms in the rate law
💡 Explanation:
Overall reaction order is found by adding together all the exponents in the experimentally determined rate law.
Q37 medium

The rate constant, k, of a reaction depends on
1. A Concentration of reactants only
2. B Volume of container
3. C Temperature (and the presence of a catalyst)
4. D Time elapsed
💡 Explanation:
The rate constant is affected by temperature and catalysts, but not by reactant concentration.
Q38 Past Paper · PPSC/FPSC/NTS medium

The Arrhenius equation relates the rate constant k to the
1. A Concentration of products
2. B Order of reaction only
3. C Equilibrium constant
4. D Temperature and activation energy
💡 Explanation:
The Arrhenius equation expresses k as a function of temperature and activation energy.
Q39 medium

The half-life of a first-order reaction is
1. A Independent of the initial concentration of reactant
2. B Directly proportional to initial concentration
3. C Inversely proportional to initial concentration
4. D Equal to zero
💡 Explanation:
A defining feature of first-order kinetics is that half-life remains constant regardless of starting concentration.
Q40 medium

Radioactive decay follows ___ order kinetics
1. A First
2. B Second
3. C Zero
4. D Third
💡 Explanation:
Radioactive decay is a classic example of a first-order kinetic process.
Q41 Past Paper · PPSC/FPSC/NTS medium

The rate-determining step of a multi-step reaction mechanism is the
1. A Fastest step
2. B First step always
3. C Last step always
4. D Slowest step, which controls the overall rate
💡 Explanation:
The slowest step in a mechanism acts as a bottleneck, controlling the overall observed rate.
Q42 medium

A transition state (activated complex) is
1. A A high-energy, unstable, transient arrangement of atoms during a reaction
2. B A stable intermediate that can be isolated
3. C The same as a catalyst
4. D The final product of a reaction
💡 Explanation:
The transition state is a fleeting, high-energy configuration at the peak of the energy barrier.
Q43 medium

Which of the following would increase the frequency of effective collisions between reactant molecules
1. A Increasing temperature
2. B Decreasing concentration
3. C Decreasing surface area
4. D Removing the catalyst
💡 Explanation:
Higher temperature increases molecular speed and energy, raising the frequency of effective collisions.
Q44 Past Paper · PPSC/FPSC/NTS medium

A reaction intermediate, unlike a transition state, is
1. A Never formed during a reaction
2. B The same as activation energy
3. C Always the final product
4. D A species that is formed and then consumed during the reaction mechanism, with a finite lifetime
💡 Explanation:
Reaction intermediates are actual, if short-lived, chemical species formed and consumed during the mechanism.
Q45 medium

The units of a rate constant depend on the
1. A Overall order of the reaction
2. B Temperature only
3. C Volume of the container
4. D Nature of the catalyst
💡 Explanation:
Rate constant units vary systematically depending on the overall order of the reaction.
Q46 Past Paper · PPSC/FPSC/NTS hard

Pseudo first-order reactions appear to follow first-order kinetics because
1. A All reactants are in equal concentration
2. B One reactant is present in large excess so its concentration remains effectively constant
3. C The reaction has no rate-determining step
4. D The catalyst controls the entire rate
💡 Explanation:
When one reactant is in large excess, its concentration barely changes, making the reaction appear first-order in the other reactant.

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