Past exam of the chemistry course of the year 1 of the natural sciences course of the University of Cambridge / 2022 / Paper 1 / 6 / a / iv / Solution

Heating increases the monomer fraction through $\mathrm{A}{\mathrm{l}}_2\mathrm{C}{\mathrm{l}}_6(\mathrm{g})\rightleftharpoons 2AlC{\mathrm{l}}_3(\mathrm{g})$. Dissociation breaks the bridge interactions and gains translational entropy by making two gas molecules from one. Its enthalpy cost becomes easier to offset at higher temperature. The qualitative statement concerns the molecular gas-phase equilibrium at the stated conditions, rather than every solid or liquid phase of aluminium chloride.