# Chemical Reaction Engineering Questions and Answers – Kinetics of Homogeneous Reactions – Comparison of Theories – 1

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This set of Chemical Reaction Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Kinetics of Homogeneous Reactions – Comparison of Theories – 1”.

1. The equation representing the variation of rate constant with respect to temperature by Arrhenius equation is ____
a) ln($$\frac{k_2}{k_1}$$) = –$$\frac{E}{R} (\frac{1}{T_2} – \frac{1}{T_1})$$
b) ln($$\frac{k_2}{k_1}$$) = $$\frac{E}{R} (\frac{1}{T_2} – \frac{1}{T_1})$$
c) ln($$\frac{k_2}{k_1}$$) = –$$\frac{E}{R} (\frac{1}{T_1}- \frac{1}{T_2})$$
d) ln($$\frac{k_2}{k_1}$$) = –$$\frac{E}{R} (\frac{1}{T_2} + \frac{1}{T_1})$$

Explanation: By Arrhenius equation, k = $$Ae^{\frac{-Ea}{RT}},$$ where A is the frequency factor.
For two different temperatures, T1 and T2, the Arrhenius equation is reduced as ln($$\frac{k_2}{k_1}$$) = –$$\frac{E}{R}(\frac{1}{T_2} – \frac{1}{T_1}).$$

2. For an endothermic reaction, the average energy of products is ____
a) Equal to the average energy of reactants
b) Lower than or equal to the average energy of reactants
c) Lower than the average energy of reactants
d) Greater than the average energy of reactants

Explanation: In an endothermic reaction, reactants absorb energy to form products. Hence, the average energy of products is greater than the average energy of reactants.

3. Collision theory states that ____
a) Molecules do not collide during the reaction
b) Reactant molecules collide to effect product formation
c) Reactants form complexes
d) Products formed are unstable

Explanation: Collision Theory states that there occur collisions between the reactant molecules. The collisions in which the molecules possess a minimum energy are effective.

4. The temperature dependency of rate constant as given by Collision theory is ____
a) k α T
b) k α T2
c) k α T3
d) k α T0.5

Explanation: According to Collision theory, k α T0.5$$e^{\frac{Ea}{RT}}$$
Where, Ea is the activation energy.
Hence the rate constant, k α T0.5.

5. State true or false.
Transition state theory shows that there exists no equilibrium between activated complex and reacting molecules at all times.
a) True
b) False

Explanation: There exists equilibrium between activated complex and reacting molecules at all times. The rate of decomposition of the complex is same for all reactions.

6. The temperature dependency of rate constant as given by Transition state theory is ____
a) k α T
b) k α T2
c) k α T3
d) k α T0.5

Explanation: According to Transition state theory, k α T$$e^{\frac{Ea}{RT}}$$. k is a linear function of temperature.

7. State true or false.
Transition state theory postulates that the reacting molecules form unstable intermediates, which are subsequently decomposed to products.
a) True
b) False

Explanation: Transition state theory proposes that reactants form intermediates called activated complex, which then stabilizes by product formation.
A + B → AB* → Products

8. If kB is Boltzmann constant and h is Plank’s constant, the rate of decomposition of complex formed during product formation, as given by Transition state theory is ____
a) $$\frac{k_B T}{h}$$
b) $$\frac{k_B h}{T}$$
c) $$\frac{k_B T}{2h}$$
d) $$\frac{k_B T^2}{h}$$

Explanation: The rate of decomposition of the complex is the same for all reactions. Decomposition rate is given as, r = $$\frac{k_B T}{h}$$.

9. Which of the following is incorrect about Transition state theory?
a) It is based on statistical mechanics
b) The formation of activated complex to be rapid
c) The decomposition of activated complex is slow
d) The formation of activated complex is the rate determining step

Explanation: The activated complex formation step is the fastest. The rate determining step is the slowest of all the steps involved in a reaction. Hence, the decomposition of activated complex is the rate determining step.

10. The minimum energy required by the reactants to effect the product formation is termed as _____
a) Threshold energy
b) Potential energy
c) Activation energy
d) Kinetic energy