Question

Assertion :A catalyst does not alter the equilibrium constant of a reaction. Reason: The catalyst forms a complex with the reactants and provides an alternate path with lower energy of activation for the reaction; the forward and back ward reactions are affected to the same extent.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Both Assertion and Reason are incorrect

Answer 1

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

A catalyst is a substance which increases the rate of reaction without itself being consumed at the end of the reaction and the phenomenon is called catalysis. There are some catalysts which decrease the rate of reaction and such catalysts are called negative catalyst. Obviously, the catalyst accelerating the rate will be positive catalyst. However, the term positive is seldom used and catalyst itself implies positive catalyst. Catalysts are generally foreign substances but sometimes one of the product formed may act as a catalyst and such a catalyst is called "auto catalyst" and the phenomenon is called auto catalysis.

Characteristics of Catalysis :

(i) A Catalyst remains unchanged in mass and chemical compositions at the end of reactions. However its physical state can be change.

(ii) Finely devided state of catalyst is more efficient for the reactions because surface area increases and more adsorption take place.

(iii) A small amount of catalyst is generally sufficient to catalyse almost unlimited reaction but in some cases the rate of reaction depends on amount of catalyst.

(iv) A catalyst cannot initiate reaction. But some times the activation energy is so large that practically a reaction may not start until a catalyst lowers the activation energy significantly. For example, mixture of hydrogen and oxygen do not react at room temperature but the reaction occurs very rapid in presence of Pt black.

(v) Catalyst are generally specific in nature. A substance which act as a catalyst in a particular reaction, fails to catalyse other reaction.

(vi) Catalyst cannot change equilibrium state but it help to attain equilibrium quickly.

The catalyst forms a complex with the reactants and provides an alternate path with lower energy of activation for the reaction; the forward and back ward reactions are affected to the same extent.

(vii) A catalyst does not change the enthalpy, entropy and free energy of a reaction.

(viii) Optimum temperature : There is a particular temperature at which the efficiency of a catalyst a maximum this temperature is known as optimum temperature. On either side the optimum temperature, the activity of catalyst decreases.