Entropy and energetics

Sample questions

Original practice questions written in the style of the exam.

1. Question 14 marks

   For the thermal decomposition of calcium carbonate,

   $\text{CaCO}_3(\text{s}) \rightarrow \text{CaO}(\text{s}) + \text{CO}_2(\text{g})$

   $\Delta H = +178\,\text{kJ mol}^{-1}$ and $\Delta S_\text{system} = +161\,\text{J K}^{-1}\,\text{mol}^{-1}$.

   Calculate the minimum temperature, in K, at which this reaction becomes thermodynamically feasible.

   Mark scheme

   • The reaction is feasible when $\Delta S_\text{total} = \Delta S_\text{system} - \dfrac{\Delta H}{T} \geq 0$ (or ) (1)
2. Question 24 marks

   Use the data below to calculate the lattice energy of calcium chloride, $\text{CaCl}_2$.

   process	$\Delta H$ / $\text{kJ mol}^{-1}$