The thermal decomposition of solid ammonium chloride is described by the equation below:
NH4Cl(s)⇌NH3(g)+HCl(g)ΔH=+176 kJ mol−1 \text{NH}_4\text{Cl}(\text{s}) \rightleftharpoons \text{NH}_3(\text{g}) + \text{HCl}(\text{g}) \quad \Delta H = +176\text{ kJ mol}^{-1} NH4Cl(s)⇌NH3(g)+HCl(g)ΔH=+176 kJ mol−1Some standard entropies are given in the table below:
| Substance | S∘ / J K−1 mol−1S^\circ \ / \ \text{J K}^{-1}\text{ mol}^{-1}S∘ / J K−1 mol−1 |
|---|---|
| NH4Cl(s)\text{NH}_4\text{Cl}(\text{s})NH4Cl(s) | 95 |
| NH3(g)\text{NH}_3(\text{g})NH3(g) | 193 |
| HCl(g)\text{HCl}(\text{g})HCl(g) | 187 |
Calculate the standard entropy change (ΔS∘\Delta S^\circΔS∘) for this reaction.
Calculate the Gibbs free-energy change (ΔG\Delta GΔG), in kJ mol−1\text{kJ mol}^{-1}kJ mol−1, for this reaction at 350 ∘C350\,^\circ\text{C}350∘C. (If you were unable to obtain an answer for Part (a), use a value of +200 J K−1 mol−1+200\text{ J K}^{-1}\text{ mol}^{-1}+200 J K−1 mol−1 for the entropy change. This is not the correct answer.)
The reaction is carried out at a higher temperature. Explain how this change in temperature affects the value of ΔG\Delta GΔG for the reaction.
