---
title: "A student evaluating mineral deposits in a heated water-treatment line studies the hypothetical sparingly soluble salt \\(\\text{MX(s)}\\). At each temperature, excess solid is allowed to reach equilibrium with pure water according to the following equation.  \\(\\text{MX(s)} \\rightleftharpoons \\text{M}^{2+}\\text{(aq)}+\\text{X}^{2-}\\text{(aq)}\\)  | Quantity | Value | |—|—| | \\(\\Delta H^\\circ_{\\text{soln}}\\) | \\(+60.0\\text{ kJ mol}^{-1}\\) | | \\(\\Delta S^\\circ_{\\text{soln}}\\) | \\(+80.0\\text{ J mol}^{-1}\\text{ K}^{-1}\\) |  Assume that \\(\\Delta H^\\circ_{\\text{soln}}\\) and \\(\\Delta S^\\circ_{\\text{soln}}\\) remain constant from \\(298\\text{ K}\\) to \\(318\\text{ K}\\). Which statement correctly compares the equilibrium molar solubility at \\(318\\text{ K}\\) with that at \\(298\\text{ K}\\) and justifies the comparison?"
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url: "https://nerd-notes.com/ubq/119495/"
date_modified: "2026-08-19T12:40:45+00:00"
---

# A student evaluating mineral deposits in a heated water-treatment line studies the hypothetical sparingly soluble salt \(\text{MX(s)}\). At each temperature, excess solid is allowed to reach equilibrium with pure water according to the following equation.

\(\text{MX(s)} \rightleftharpoons \text{M}^{2+}\text{(aq)}+\text{X}^{2-}\text{(aq)}\)

| Quantity | Value |
|—|—|
| \(\Delta H^\circ_{\text{soln}}\) | \(+60.0\text{ kJ mol}^{-1}\) |
| \(\Delta S^\circ_{\text{soln}}\) | \(+80.0\text{ J mol}^{-1}\text{ K}^{-1}\) |

Assume that \(\Delta H^\circ_{\text{soln}}\) and \(\Delta S^\circ_{\text{soln}}\) remain constant from \(298\text{ K}\) to \(318\text{ K}\). Which statement correctly compares the equilibrium molar solubility at \(318\text{ K}\) with that at \(298\text{ K}\) and justifies the comparison?

A student evaluating mineral deposits in a heated water-treatment line studies the hypothetical sparingly soluble salt \(\text{MX(s)}\). At each temperature, excess solid is allowed to reach equilibrium with pure water according to the following equation.

\(\text{MX(s)} \rightleftharpoons \text{M}^{2+}\text{(aq)}+\text{X}^{2-}\text{(aq)}\)

| Quantity | Value |
|---|---|
| \(\Delta H^\circ_{\text{soln}}\) | \(+60.0\text{ kJ mol}^{-1}\) |
| \(\Delta S^\circ_{\text{soln}}\) | \(+80.0\text{ J mol}^{-1}\text{ K}^{-1}\) |

Assume that \(\Delta H^\circ_{\text{soln}}\) and \(\Delta S^\circ_{\text{soln}}\) remain constant from \(298\text{ K}\) to \(318\text{ K}\). Which statement correctly compares the equilibrium molar solubility at \(318\text{ K}\) with that at \(298\text{ K}\) and justifies the comparison?

- **A.** The solubility decreases, because the positive \(\Delta H^\circ_{\text{soln}}\) means that heating makes the dissolution less thermodynamically favorable.
- **B.** The solubility decreases, because increasing \(T\) makes \(T\Delta S^\circ_{\text{soln}}\) larger and therefore makes \(\Delta G^\circ_{\text{soln}}\) larger.
- **C.** The solubility increases, because heating changes \(\Delta H^\circ_{\text{soln}}\) from positive to negative.
- **D.** The solubility increases, because \(-T\Delta S^\circ_{\text{soln}}\) becomes more negative while \(\Delta H^\circ_{\text{soln}}\) remains approximately constant, so \(\Delta G^\circ_{\text{soln}}\) decreases.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/119495/*