Activation energy of reverse reaction = E_a,f - ΔH_f

Steps:

• Note forward reaction is exothermic since ΔH_f = -50 kJ/mol.
• Recall formula for reversible reactions: E_a,reverse = E_a,forward - ΔH_f.
• Substitute values: E_a,r = 60 kJ/mol - (-50 kJ/mol) = 60 + 50 = 110 kJ/mol.
• Confirm result matches option D.

Why D is correct:

• Follows the definition that activation energy difference equals enthalpy change, per energy diagram principles.

Why the others are wrong:

• A and B: Negative values impossible for activation energy, which is always positive.
• C: Equals |ΔH_f|, ignoring addition to forward E_a.

Final answer: D