---
title: "A thermodynamic evaluation is conducted on four industrial chemical reactions. The standard enthalpy change, \\(\\Delta H^\\circ\\), and standard entropy change, \\(\\Delta S^\\circ\\), for each reaction at \\(298 \\text{ K}\\) are shown in the table below.  | Reaction | Chemical equation | \\(\\Delta H^\\circ\\ (\\text{kJ/mol}_{\\text{rxn}})\\) | \\(\\Delta S^\\circ\\ (\\text{J}/(\\text{mol}_{\\text{rxn}}\\cdot\\text{K}))\\) | | :— | :— | :— | :— | | 1 | \\(\\text{N}_2\\text{O}_4\\text{(g)} \\rightarrow 2\\,\\text{NO}_2\\text{(g)}\\) | \\(+60\\) | \\(+200\\) | | 2 | \\(\\text{PCl}_5\\text{(g)} \\rightarrow \\text{PCl}_3\\text{(g)} + \\text{Cl}_2\\text{(g)}\\) | \\(+100\\) | \\(+200\\) | | 3 | \\(\\text{CaCO}_3\\text{(s)} \\rightarrow \\text{CaO(s)} + \\text{CO}_2\\text{(g)}\\) | \\(+180\\) | \\(+225\\) | | 4 | \\(\\text{C(s)} + \\text{H}_2\\text{O(g)} \\rightarrow \\text{CO(g)} + \\text{H}_2\\text{(g)}\\) | \\(+120\\) | \\(+100\\) |  Assuming that \\(\\Delta H^\\circ\\) and \\(\\Delta S^\\circ\\) remain constant with changing temperature, which of the following correctly ranks the reactions in order of increasing minimum temperature at which each reaction becomes thermodynamically favorable under standard conditions (\\(\\Delta G^\\circ < 0\\))?"
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date_modified: "2026-09-28T12:32:17+00:00"
---

# A thermodynamic evaluation is conducted on four industrial chemical reactions. The standard enthalpy change, \(\Delta H^\circ\), and standard entropy change, \(\Delta S^\circ\), for each reaction at \(298 \text{ K}\) are shown in the table below.

| Reaction | Chemical equation | \(\Delta H^\circ\ (\text{kJ/mol}_{\text{rxn}})\) | \(\Delta S^\circ\ (\text{J}/(\text{mol}_{\text{rxn}}\cdot\text{K}))\) |
| :— | :— | :— | :— |
| 1 | \(\text{N}_2\text{O}_4\text{(g)} \rightarrow 2\,\text{NO}_2\text{(g)}\) | \(+60\) | \(+200\) |
| 2 | \(\text{PCl}_5\text{(g)} \rightarrow \text{PCl}_3\text{(g)} + \text{Cl}_2\text{(g)}\) | \(+100\) | \(+200\) |
| 3 | \(\text{CaCO}_3\text{(s)} \rightarrow \text{CaO(s)} + \text{CO}_2\text{(g)}\) | \(+180\) | \(+225\) |
| 4 | \(\text{C(s)} + \text{H}_2\text{O(g)} \rightarrow \text{CO(g)} + \text{H}_2\text{(g)}\) | \(+120\) | \(+100\) |

Assuming that \(\Delta H^\circ\) and \(\Delta S^\circ\) remain constant with changing temperature, which of the following correctly ranks the reactions in order of increasing minimum temperature at which each reaction becomes thermodynamically favorable under standard conditions (\(\Delta G^\circ < 0\))?

A thermodynamic evaluation is conducted on four industrial chemical reactions. The standard enthalpy change, \(\Delta H^\circ\), and standard entropy change, \(\Delta S^\circ\), for each reaction at \(298 \text{ K}\) are shown in the table below.

| Reaction | Chemical equation | \(\Delta H^\circ\ (\text{kJ/mol}_{\text{rxn}})\) | \(\Delta S^\circ\ (\text{J}/(\text{mol}_{\text{rxn}}\cdot\text{K}))\) |
| :--- | :--- | :--- | :--- |
| 1 | \(\text{N}_2\text{O}_4\text{(g)} \rightarrow 2\,\text{NO}_2\text{(g)}\) | \(+60\) | \(+200\) |
| 2 | \(\text{PCl}_5\text{(g)} \rightarrow \text{PCl}_3\text{(g)} + \text{Cl}_2\text{(g)}\) | \(+100\) | \(+200\) |
| 3 | \(\text{CaCO}_3\text{(s)} \rightarrow \text{CaO(s)} + \text{CO}_2\text{(g)}\) | \(+180\) | \(+225\) |
| 4 | \(\text{C(s)} + \text{H}_2\text{O(g)} \rightarrow \text{CO(g)} + \text{H}_2\text{(g)}\) | \(+120\) | \(+100\) |

Assuming that \(\Delta H^\circ\) and \(\Delta S^\circ\) remain constant with changing temperature, which of the following correctly ranks the reactions in order of increasing minimum temperature at which each reaction becomes thermodynamically favorable under standard conditions (\(\Delta G^\circ < 0\))?

- **A.** \(\text{Reaction 1} < \text{Reaction 2} < \text{Reaction 3} < \text{Reaction 4}\)
- **B.** \(\text{Reaction 1} < \text{Reaction 2} < \text{Reaction 4} < \text{Reaction 3}\)
- **C.** \(\text{Reaction 4} < \text{Reaction 3} < \text{Reaction 2} < \text{Reaction 1}\)
- **D.** \(\text{Reaction 4} < \text{Reaction 2} < \text{Reaction 1} < \text{Reaction 3}\)

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/123929/*