The enthalpy change of a reaction ($\Delta H$) is equal to the difference between the activation energy of the forward reaction ($E_{a(\text{forward})}$) and the activation energy of the reverse/backward reaction ($E_{a(\text{reverse})}$). This relationship can be expressed as: $\Delta H = E_{a(\text{forward})} - E_{a(\text{reverse})}$ Given that the activation energies for both the forward and reverse reactions are equal ($E_{a(\text{forward})} = E_{a(\text{reverse})}$), their difference becomes zero. Therefore, $\Delta H = 0$.