Question

A catalyst increases the rate of reaction by:

A. Increasing the activation energy of the reaction.

B. Increasing the value of rate constants ($K_f$ and $K_b$).

C. Increasing the enthalpy change of the reaction.

D. Decreasing the enthalpy change of the reaction.

Answer 1

Hint: A catalyst increases the rate of reaction by decreasing the activation energy.

According to collision theory effective collision between the molecules results in a reaction. For effective collision to occur molecules must have a minimum amount of energy. This energy is known as threshold energy. So for a reaction to occur molecules must have energy greater than threshold energy.

Complete step by step answer:

- The difference between average internal energy and threshold energy is known as activation energy. This is the extra energy that the reactant molecules must acquire to cross the activation barrier.

- A catalyst is used to accelerate the rate of a reaction and without being consumed. The function of a catalyst is to lower the activation energy. It speeds up the rate of both forward and backward reaction to the same extent so it can’t affect the position of equilibrium.

- A catalyst increases the rate of reaction by decreasing activation energy. and increasing the enthalpy change of the reaction

- A catalyst can lower the energy barrier by orienting the reacting particles in the proper manner for effective collision and reacting with reactants to form an activated complex. In the presence of a catalyst, the activation energy has decreased. So the reactant molecules can easily cross the energy barrier and convert into products. Hence the rate of the reaction increases with a catalyst.

Therefore, the correct answer is (C) i.e increasing the enthalpy change of the reaction.

Note:

Since the 1950s chemicals have been produced from coal. Coal gasification to produce syngas is the main route of these products. Coal can be used as a feedstock in the production of a wide range of chemical fertilizers and other chemical products.