Activation energies differ by enthalpy change in reversible reactions Steps:

• Backward reaction endothermic: ΔH_backward = +160 kJ mol⁻¹, so ΔH_forward = -160 kJ mol⁻¹.
• Mechanism is exact reverse, so same transition states; energy diagram shows Ea_backward = Ea_forward - ΔH_forward.
• Substitute ΔH_forward: Ea_backward = Ea_forward + 160 kJ mol⁻¹.
• Rearrange: Ea_forward = Ea_backward - 160 kJ mol⁻¹ (160 kJ mol⁻¹ less than backward activation energy).

Why B is correct:

• Matches the relation Ea_forward = Ea_backward + ΔH_forward from potential energy diagrams for reversible reactions.

Why the others are wrong:

• A: Activation energies cannot be negative, as they are energy barriers above reactants.
• C: Ea_forward equals +160 kJ mol⁻¹ only if Ea_backward = 320 kJ mol⁻¹, not generally true.
• D: Ea_forward could be less than +160 kJ mol⁻¹ (e.g., if Ea_backward = 200 kJ mol⁻¹, then 40 kJ mol⁻¹).

Final answer: B