The enthalpy changes of formation, $\Delta H_f^\circ$, for both $\text{PCl}_3$ and $\text{PCl}_5$ are exothermic. $\text{PCl}_3$ undergoes reaction with chlorine. $\text{PCl}_3(\ell) + \text{Cl}_2(g) \rightarrow \text{PCl}_5(s) \qquad \Delta H_{reaction}^\circ = -124\,\text{kJ mol}^{-1}$. Which pair of statements is correct?
Chemistry 9701 · AS & A Level · Chemical energetics