If a catalyst changes the activation energy of a forward reaction from 28.0 kcal/mol to 23.0 kcal/mol, what effect does it have on the reverse reaction?

For an equilibrium reaction, the rate of forward reaction is equal to the rate of backward reaction.

As in the given reaction, change in activation energy is as follows.

(28.0 - 23.0) kcal/mol

= 5 kcal/mol

Therefore, when activation energy is increasing 5 kcal/mol for the given reaction in the forward direction then for the backward reaction there will be be a decrease of 5 kcal/mol.

Thus, we can conclude that if a catalyst changes the activation energy of a forward reaction from 28.0 kcal/mol to 23.0 kcal/mol, then it reduces the energy of activation of the reverse reaction by 5.0 kcal/mol.

Activation energy (Ea) is the minimum energy required by the reactants so that they can overcome the energy barrier to form corresponding products.

The role of a catalyst is to lower this energy barrier and speed up the rate of the reaction. For a reaction at equilibrium, a catalyst tends to speed up both the forward and reverse reaction in the same ratio.

In this case, the Ea for the forward reaction decreases from 28.0 kcal/mol to 23.0 kcal/mol. The change in Ea for the forward reaction is: ΔEa = 5 kcal/mol. In a similar manner the Ea for the reverse reaction will also be lowered by 5 kcal/mol.