= Solution
\b[The products lie below the reactants, while the <transition state> lies above both.] On an energy-versus-reaction-coordinate plot, the forward <activation energy> is the vertical separation $E_{\rm TS}-E_{\rm R}$, not the difference between product and reactant energies. For an exothermic elementary path, $\Delta E=E_{\rm P}-E_{\rm R}<0$, and the reverse barrier is $E_{a,-}=E_{a,+}-\Delta E>E_{a,+}$.
\Image[/past-exam-of-the-chemistry-course-of-the-year-1-of-the-natural-sciences-course-of-the-university-of-cambridge/2023/paper-1-exothermic-profile.png]
{title=Original schematic exothermic energy profile with reactant, product, transition-state and forward-barrier labels}
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