AP Chemistry
9.6 Free Energy of Dissolution
9.3 Gibbs Free Energy and Thermodynamic Favorability
A student investigates the dissolution of a sparingly soluble ionic compound, \(\text{MX}_2(s)\), in pure water according to the following process:
\[ \text{MX}_2(s) \rightleftharpoons \text{M}^{2+}(aq) + 2\,\text{X}^-(aq) \quad \Delta H^\circ_{\text{soln}} > 0 \]
At \(298\text{ K}\), both \(\Delta G^\circ_{\text{soln}} > 0\) and \(\Delta S^\circ_{\text{soln}} > 0\). The temperature of the saturated solution containing excess undissolved \(\text{MX}_2(s)\) is increased from \(298\text{ K}\) to \(350\text{ K}\). Assuming \(\Delta H^\circ_{\text{soln}}\) and \(\Delta S^\circ_{\text{soln}}\) are independent of temperature over this range, which of the following correctly predicts the effect on the thermodynamic favorability of the dissolution process and provides the correct justification?
\[ \text{MX}_2(s) \rightleftharpoons \text{M}^{2+}(aq) + 2\,\text{X}^-(aq) \quad \Delta H^\circ_{\text{soln}} > 0 \]
At \(298\text{ K}\), both \(\Delta G^\circ_{\text{soln}} > 0\) and \(\Delta S^\circ_{\text{soln}} > 0\). The temperature of the saturated solution containing excess undissolved \(\text{MX}_2(s)\) is increased from \(298\text{ K}\) to \(350\text{ K}\). Assuming \(\Delta H^\circ_{\text{soln}}\) and \(\Delta S^\circ_{\text{soln}}\) are independent of temperature over this range, which of the following correctly predicts the effect on the thermodynamic favorability of the dissolution process and provides the correct justification?
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