Past exam of the chemistry course of the year 1 of the natural sciences course of the University of Cambridge / 2022 / Paper 1 / 5 / b / i / Solution

The forward and reverse pathways pass through the same transition state. Measured from the cis minimum, the forward barrier is $E_{a,1}$; measured from the trans minimum, the reverse barrier is $E_{a,-1}$. Since $E_{a,-1}=E_{a,1}+2.23\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$, the trans minimum lies $2.23\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$ below the cis minimum in the elementary energy-profile model:The absolute barrier heights cannot be deduced from their difference. The following original profile uses an arbitrary transition-state height and labels that distinction explicitly.