Read the Passage carefully and answer the Questions.
Kinetic studies not only help us to determine the rate of a chemical reaction but also describe the conditions by which the reaction rates can be altered. The factors such as concentration, temperature, pressure and catalyst affect the rate of a reaction. The speed of a reaction or the rate of a reaction can be defined as the change in concentration of a reactant or product in unit time.
Rate = $k [A]^x [B]^y$
Here k is the rate constant
$x + y$ gives the overall order of a reaction, whereas x and y represent the order with respect to the reactants A and B, respectively.
Which of the following statements are correct?
(A) Catalysts increase the rate of a chemical reaction.
(B) Catalysts can catalyze both spontaneous and non-spontaneous reactions.
(C) Higher the activation energy for a chemical reaction, lower is the rate of the reaction.
(D) Catalyst increases the potential energy barrier.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A) and (C) only
(A) Catalysts increase the rate of a chemical reaction.
- Correct. A catalyst provides an alternate reaction pathway with a lower activation energy, thus increasing the rate of the reaction.
(B) Catalysts can catalyze both spontaneous and non-spontaneous reactions.
- Incorrect. A catalyst affects only the rate of a reaction; it does not change the Gibbs free energy (ΔG) of the reaction. Since spontaneity is determined by ΔG, a catalyst can only accelerate a reaction that is already thermodynamically feasible (spontaneous, ΔG<0). It cannot make a non-spontaneous reaction (ΔG>0) spontaneous.
(C) Higher the activation energy for a chemical reaction, lower is the rate of the reaction.
- Correct. The activation energy ($E_a$) is the minimum energy required for reactant molecules to transform into products. According to the Arrhenius equation, the reaction rate is exponentially and inversely related to the activation energy. A higher $E_a$ means fewer molecules possess the required energy barrier, leading to a smaller rate constant (k) and a lower reaction rate.
(D) Catalyst increases the potential energy barrier.
- Incorrect. This is the opposite of the function of a catalyst. A catalyst works by decreasing the potential energy barrier (activation energy) of the reaction.
Conclusion
The correct statements are (A) and (C).