Interpreting Reaction Energy Profiles

Steps:

• Compare reactant and product energy levels: if products are lower, the reaction is exothermic.
• Locate the transition state at the profile's peak energy.
• Activation energy (Ea) is the energy difference from reactants to the transition state peak.
• Match labels: P as reactant energy, R as peak (transition state), Q as product energy (lower than P).

Why B is correct:

• Exothermic reactions release energy (products lower than reactants, per ΔH < 0 definition); Ea = P-R matches the barrier from reactants (P) to peak (R).

Why the others are wrong:

• A: Incorrectly labels as endothermic (products not higher).
• C: Wrong type (endothermic) and Ea (Q-R misidentifies barrier).
• D: Correct type but wrong Ea (R-P reverses direction, yielding negative value).

Final answer: B