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For a reversible endothermic reaction , the overall enthalpy change is . If the activation energy ofChemical Kinetics Chemistry Question

Question

For a reversible endothermic reaction $A \rightarrow B$, the overall enthalpy change is $\Delta H = +20 \text{ kJ/mol}$. If the activation energy of the forward reaction is $E_{a(f)} = 85 \text{ kJ/mol}$, calculate the backward activation energy $E_{a(b)}$.

Answer: B

💡 Solution & Explanation

The fundamental thermodynamic relationship is $\Delta H = E_{a(f)} - E_{a(b)}$. Substituting the known values yields $+20 = 85 - E_{a(b)}$. Rearranging immediately provides $E_{a(b)} = 85 - 20 = 65 \text{ kJ/mol}$.

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