Question

What is the activation energy for the reverse reaction in terms of the activation energy of the forward reaction and the enthalpy of reaction? Draw it out for an endothermic reaction.

Answer 1

This is asking you to draw a potential energy diagram for an endothermic reaction.

Recall that `DeltaH_"rxn"`, the enthalpy of reaction, is positive for endothermic reactions, i.e. the product(s) (right) are higher in energy than the reactant(s) (left) and energy was absorbed.

(Energy increases from bottom to top.)

Since...

• the activation energy for the forward reaction is the difference in energy between the reactant(s) (left) and the transition state (hill)
• the enthalpy of reaction is the difference in energy between the product(s) (right) and reactant(s) (left)

...the activation energy of the reverse reaction is just the difference in energy between the product(s) (right) and the transition state (hill).

Thus, for this endothermic reaction, `\mathbf(E_(a,"rev") = E_(a,"fwd") - DeltaH_"rxn")`. To apply this process to other reactions, draw out the correct diagram and try working it out visually.