Question

For a reaction A \( \rightarrow \) B; \( \Delta H = 20 \, \text{kJ mol}^{-1} \), the activation energy of the forward reaction is 85 kJ/mol. The activation energy of the backward reaction will be

• A. 105 kJ/mol
• B. 65 kJ/mol
• C. 45 kJ/mol
• D. 75 kJ/mol

Hint:

The activation energy of the backward reaction is the sum of the activation energy of the forward reaction and the enthalpy change.

Answer 1

The Correct Option is A

Step 1: Activation Energy of Backward Reaction.
The activation energy of the backward reaction can be found using the formula: \[ E_a (\text{backward}) = E_a (\text{forward}) + \Delta H \] where \( E_a (\text{forward}) = 85 \, \text{kJ/mol} \) and \( \Delta H = 20 \, \text{kJ/mol} \). Thus: \[ E_a (\text{backward}) = 85 + 20 = 105 \, \text{kJ/mol}. \] Step 2: Conclusion.
The correct answer is (A), 105 kJ/mol.