Question

Which of the following explains the increase of the reaction rate by catalyst ?

• A. Catalyst decreases the rate of backward reaction so that the rate of forward reaction increases.
• B. Catalyst provides extra energy to reacting molecules so that they may produce effective collisions.
• C. Catalyst provides an alternative path o lower activation energy to the reactants.
• D. Catalyst increases the number of collisions between the reacting molecules.

Answer 1

Answer: (C)

Catalyst provides an alternative path o lower activation energy to the reactants.

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.

Characteristics of catalyst are as follows:

i) A catalyst remains unchanged chemically at the end of reaction, however its physical state may change.

ii) A catalyst never initiate a chemical reaction. It simply influences the rate of reaction.

iii) A small quantity of catalyst is sufficient to influence the rate of reaction

iv) A catalyst does not influence the equilibrium constant of reaction. It simply helps in attaining equilibrium earlier. It alters the rate of forward & backward reactions equally.

v) Catalyst’s activity is more or less specific.

A catalyst for one reaction is not necessary to catalyse the another reaction.