Chemical Kinetics

Chemical Kinetics MDCAT MCQs with answers

21 past paper MCQs on Chemical Kinetics, from the Reaction Kinetics unit of MDCAT Chemistry. The year each question appeared is shown where known; tap “Show answer” for the correct option and a short solution.

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1.The rate of a reaction: (MDCAT 2020)

  1. increases as the reaction proceeds
  2. decreases as the reaction proceeds
  3. remains the same
  4. may decrease or increase
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Correct answer: (b) decreases as the reaction proceeds

The reactants are being used up, so their concentrations and with them the rate fall as the reaction goes on.

2.The rate of reaction between two specific time intervals is called the: (MDCAT 2023)

  1. instantaneous rate of reaction
  2. rate of reaction
  3. average rate of reaction
  4. specific rate of reaction
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Correct answer: (c) average rate of reaction

A change measured over an interval rather than at an instant is the average rate.

3.Identify the correct formula to calculate the rate of a reaction: (MDCAT 2024)

  1. change in concentration of substance $\div$ time taken for the change
  2. time taken for the change $\div$ change in concentration of substance
  3. time taken for the change $\div$ change in concentration $\times100$
  4. time taken for the change $\times$ change in concentration
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Correct answer: (a) change in concentration of substance $\div$ time taken for the change

Rate is the change in concentration per unit time.

4.Amount of energy needed to weaken the existing bonds to an extent that can be broken through collision is called: (UHS MDCAT 2025)

  1. Bond energy
  2. Activation energy
  3. Average energy
  4. Enthalpy
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Correct answer: (b) Activation energy

Activation energy is the least energy a colliding pair must carry for the reaction to proceed.

5.2A + B -> 3C + D which of the following does not express the reaction rate? (UHS MDCAT 2025)

  1. -d[B]/dt
  2. d[D]/dt
  3. -1/2 d[A]/dt
  4. -1/3 d[C]/dt
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Correct answer: (d) -1/3 d[C]/dt

C is formed, not consumed, so its rate term takes a plus sign.

6.Final equation for the representation of rate of reaction in term of concentration is called (UHS MDCAT 2025)

  1. Rate law
  2. Rate constant
  3. Reaction rate
  4. Reaction order
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Correct answer: (a) Rate law

The rate law is the equation giving the rate in terms of the concentrations of the reactants.

7.The formation of activated complex in a reaction is: (SIBA MDCAT 2025)

  1. Exothermic process
  2. Endothermic process
  3. Either endo or exo
  4. Always energy released
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Correct answer: (b) Endothermic process

Energy must be put in to reach the activated complex, so forming it absorbs heat.

8.At start of reaction: (SIBA MDCAT 2025)

  1. Average rate is high
  2. Instantaneous rate is high
  3. Both rates are same
  4. Both rates are slow
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Correct answer: (b) Instantaneous rate is high

At the start the concentration of reactant is greatest, so the instantaneous rate is at its highest.

9.Reaction having high activation energy are: (SZABMU MDCAT 2025)

  1. spontaneous
  2. fast
  3. slow
  4. always exothermic
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Correct answer: (c) slow

The higher the barrier, the fewer the collisions that carry enough energy, so the slower the reaction.

10.The rate of reaction (SZABMU MDCAT 2025)

  1. Increases as the reaction proceeds
  2. Decreases as the reaction proceeds
  3. Remains the same as the reaction proceeds
  4. May decrease or increase as the reaction proceeds
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Correct answer: (d) May decrease or increase as the reaction proceeds

It usually falls as the reactants are used up, but an autocatalytic reaction speeds up instead.

11.Identify the correct formula to calculate rate of reaction: (UHS MDCAT 2024)

  1. Change in concentration of substance ÷ Time taken for the change
  2. Time taken for the change ÷ Change in concentration of substance
  3. Time taken for the change ÷ Change in concentration of substance x 100
  4. Time taken for the change x Change in concentration of substance
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Correct answer: (a) Change in concentration of substance ÷ Time taken for the change

Rate is the change in concentration divided by the time it took.

12.What is incorrect about activated complex? (SZABMU MDCAT 2023)

  1. It is a high energy specie
  2. It is a stable specie
  3. It is an unstable specie
  4. Potentia energy is maximum at activated complex stage
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Correct answer: (b) It is a stable specie

The activated complex sits at the top of the energy barrier and is therefore unstable.

13.The minimum amount of energy required by the colliding particles for effective collisions is called: (NUMS MDCAT 2023)

  1. Activation energy
  2. Lattice energy
  3. Bond energy
  4. Hydration energy
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Correct answer: (a) Activation energy

That least energy is the activation energy.

14.How will be the rate of reaction, if the slope of the curve is greater near the start of the reaction? (UHS MDCAT 2023)

  1. Constant
  2. Equilibrium
  3. Greater
  4. Lesser
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Correct answer: (c) Greater

The slope of the concentration time curve is the rate, so a steep slope means a fast reaction.

15.The rate of reaction between two specific time intervals is called? (UHS MDCAT 2023)

  1. Instantaneous rate of reaction
  2. Rate of reaction
  3. Average rate of reaction
  4. Initial rate
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Correct answer: (c) Average rate of reaction

A rate measured over an interval rather than at an instant is the average rate.

16.Activation energy for forward and backward reaction is always: (PMC MDCAT 2022)

  1. Same
  2. Different
  3. Reciprocal of each other
  4. Higher for forward reaction
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Correct answer: (b) Different

The two barriers differ by the enthalpy of the reaction.

17.At ordinary temperature, only few molecules possess energy equal to (PMC MDCAT 2022)

  1. Kinetic energy
  2. Potential Energy
  3. Activation energy
  4. Ionization Energy
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Correct answer: (c) Activation energy

Only the small fraction of molecules at the top of the energy distribution can react.

18.Drawing a graph between concentration change with time gives a: (PMC Practice 2021)

  1. Straight line
  2. Parabola
  3. Curve
  4. Scattered graph
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Correct answer: (c) Curve

The rate falls as the reactant is used up, so the plot bends.

19.The study of rates of chemical reactions and the factors that affect the rates of chemical reactions is known as: (PMC MDCAT 2020)

  1. Thermodynamics
  2. Stoichiometry
  3. Electrochemistry
  4. Chemical Kinetics
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Correct answer: (d) Chemical Kinetics

That study is chemical kinetics.

20.What is the measure of activation energy in an endothermic reaction? (UHS MDCAT 2019)

  1. The energy of activation of backward reaction is less than that of forward reaction
  2. The energy of activation of backward reaction is more that that of forward reaction.
  3. The energy of activation of forward reaction is less than that of backward reaction.
  4. The energy of activation of forward – backward reaction is same.
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Correct answer: (a) The energy of activation of backward reaction is less than that of forward reaction

The products lie above the reactants, so the barrier is lower seen from the product side.

21.If the energy of activation of a chemical reaction is very low, the rate of that chemical reaction is observed to be very high because? (UHS MDCAT 2019)

  1. Concentration of the reactants becomes irrelevant
  2. Reaction proceeds without any transition state
  3. Number of efficient or fruitful collisions increase
  4. Molecules of the reactants move slowly
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Correct answer: (c) Number of efficient or fruitful collisions increase

A low barrier means a large fraction of collisions carry enough energy to succeed.

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