Question

Briefly comment on the effect of a catalyst on each of the following: (a) activation energy, (b) reaction mechanism, (c) enthalpy of reaction, (d) rate of forward step, (e) rate of reverse step.

Short answer

A catalyst decreases the activation energy, changes the reaction mechanism, has no effect on enthalpy, and increases both the rate of the forward and reverse steps.

Step-by-step solution

Implication of a Catalyst on Activation Energy

A catalyst provides an alternate path or mechanism for a reaction to follow, which has a lower activation energy than the uncatalyzed reaction. Therefore, a catalyst decreases the activation energy of a reaction.

Implication of a Catalyst on Reaction Mechanism

A catalyst doesn't change the reaction itself but provides a new mechanism or reaction path to proceed, that is, it changes the intermediary stages of the reaction while the initial and final stages remain the same.

Implication of a Catalyst on Enthalpy of Reaction

Since a catalyst doesn't change the states of the reactants and products, it has no effect on the enthalpy or heat content of the reaction. The enthalpy change (\( \Delta H\)) for a reaction remains the same whether a catalyst is used or not.

Implication of a Catalyst on Rate of Forward Step

By lowering the activation energy, a catalyst increases the rate of the forward step of a reaction, so the reaction reaches equilibrium more quickly.

Implication of a Catalyst on Rate of Reverse Step

A catalyst accelerates both the forward and reverse reactions equally, because it merely lowers the activation energy barrier. So, the rate of reverse reaction also increases when a catalyst is involved.