Analyzing Reversible Reaction Energy Profiles

Steps:

• Identify reactant and product energy levels: ΔH_forward = E_products - E_reactants.
• Calculate backward enthalpy: ΔH_backward = -ΔH_forward.
• Determine forward activation energy (E_a): energy from reactants to transition state peak.
• Compare to diagram values for endothermic/exothermic nature.

Why A is correct:

• By definition, ΔH_backward = -ΔH_forward; if forward ΔH = +20 kJ mol⁻¹ (products higher), backward is -20 kJ mol⁻¹.

Why the others are wrong:

• B: Forward is exothermic (products lower than reactants), not endothermic.
• C: Forward E_a is 30 kJ mol⁻¹ (peak 30 kJ above reactants), not 50 kJ mol⁻¹.
• D: Not enough information (option incomplete).

Final answer: A