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

Integrating the Van't Hoff equation with approximately constant reaction enthalpy givesUsing the full calculated $K_{298}=2.4596538\dots$ yieldsThe negative sign agrees with the decrease of $K$ on heating. This is the two-temperature estimate from the supplied equilibrium data. It is not exactly the $-2.23\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$ implied by treating equal prefactors and a fixed activation-energy difference as exact throughout the interval: that stricter model predicts $K_{318}=2.3243$ rather than $2.31$. The data and idealizations are therefore only approximately mutually consistent; no rounding of intermediate calculations can make both numerical enthalpy estimates identical.