The activation energy for the forward reaction X Y is 60 KJ mol−1 and ΔH is −20 KJ mol−1. The activation energy for the backward reaction Y X is:

To find the activation energy for the backward reaction Y X, we can use the relationship between activation energy and enthalpy change (ΔH) for a reaction.

The activation energy for the forward reaction X Y is given as 60 KJ mol−1. This means that in order for the reaction to proceed in the forward direction, an energy barrier of 60 KJ mol−1 must be overcome.

The enthalpy change (ΔH) for the reaction is given as −20 KJ mol−1. A negative value for ΔH indicates that the reaction is exothermic, meaning it releases energy.

For the backward reaction Y X, the activation energy can be determined using the relationship:

Activation energy (backward) = Activation energy (forward) + ΔH

Substituting the given values, we have:

Activation energy (backward) = 60 KJ mol−1 + (−20 KJ mol−1)

Simplifying, we find:

Activation energy (backward) = 40 KJ mol−1

Therefore, the activation energy for the backward reaction Y X is 40 KJ mol−1.