---
title: "A student attempts to determine the standard enthalpy change, \\(\\Delta H^\\circ_{rxn}\\), for the industrial dehydrogenation of propane to propene:  \\[\\text{C}_3\\text{H}_8\\text{(g)} \\rightarrow \\text{C}_3\\text{H}_6\\text{(g)} + \\text{H}_2\\text{(g)}\\]  The student looks up the standard enthalpies of combustion for the relevant species, as summarized in the table below.  | Reaction | Chemical Equation | Enthalpy Change | |—|—|—| | (1) | \\(\\text{C}_3\\text{H}_8\\text{(g)} + 5\\,\\text{O}_2\\text{(g)} \\rightarrow 3\\,\\text{CO}_2\\text{(g)} + 4\\,\\text{H}_2\\text{O(l)}\\) | \\(\\Delta H_1\\) | | (2) | \\(\\text{C}_3\\text{H}_6\\text{(g)} + \\dfrac{9}{2}\\,\\text{O}_2\\text{(g)} \\rightarrow 3\\,\\text{CO}_2\\text{(g)} + 3\\,\\text{H}_2\\text{O(l)}\\) | \\(\\Delta H_2\\) | | (3) | \\(\\text{H}_2\\text{(g)} + \\dfrac{1}{2}\\,\\text{O}_2\\text{(g)} \\rightarrow \\text{H}_2\\text{O(l)}\\) | \\(\\Delta H_3\\) |  Which of the following mathematical expressions correctly determines \\(\\Delta H^\\circ_{rxn}\\) for the dehydrogenation reaction?"
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url: "https://nerd-notes.com/ubq/119248/"
date_modified: "2026-08-19T12:39:32+00:00"
---

# A student attempts to determine the standard enthalpy change, \(\Delta H^\circ_{rxn}\), for the industrial dehydrogenation of propane to propene:

\[\text{C}_3\text{H}_8\text{(g)} \rightarrow \text{C}_3\text{H}_6\text{(g)} + \text{H}_2\text{(g)}\]

The student looks up the standard enthalpies of combustion for the relevant species, as summarized in the table below.

| Reaction | Chemical Equation | Enthalpy Change |
|—|—|—|
| (1) | \(\text{C}_3\text{H}_8\text{(g)} + 5\,\text{O}_2\text{(g)} \rightarrow 3\,\text{CO}_2\text{(g)} + 4\,\text{H}_2\text{O(l)}\) | \(\Delta H_1\) |
| (2) | \(\text{C}_3\text{H}_6\text{(g)} + \dfrac{9}{2}\,\text{O}_2\text{(g)} \rightarrow 3\,\text{CO}_2\text{(g)} + 3\,\text{H}_2\text{O(l)}\) | \(\Delta H_2\) |
| (3) | \(\text{H}_2\text{(g)} + \dfrac{1}{2}\,\text{O}_2\text{(g)} \rightarrow \text{H}_2\text{O(l)}\) | \(\Delta H_3\) |

Which of the following mathematical expressions correctly determines \(\Delta H^\circ_{rxn}\) for the dehydrogenation reaction?

A student attempts to determine the standard enthalpy change, \(\Delta H^\circ_{rxn}\), for the industrial dehydrogenation of propane to propene:

\[\text{C}_3\text{H}_8\text{(g)} \rightarrow \text{C}_3\text{H}_6\text{(g)} + \text{H}_2\text{(g)}\]

The student looks up the standard enthalpies of combustion for the relevant species, as summarized in the table below.

| Reaction | Chemical Equation | Enthalpy Change |
|---|---|---|
| (1) | \(\text{C}_3\text{H}_8\text{(g)} + 5\,\text{O}_2\text{(g)} \rightarrow 3\,\text{CO}_2\text{(g)} + 4\,\text{H}_2\text{O(l)}\) | \(\Delta H_1\) |
| (2) | \(\text{C}_3\text{H}_6\text{(g)} + \dfrac{9}{2}\,\text{O}_2\text{(g)} \rightarrow 3\,\text{CO}_2\text{(g)} + 3\,\text{H}_2\text{O(l)}\) | \(\Delta H_2\) |
| (3) | \(\text{H}_2\text{(g)} + \dfrac{1}{2}\,\text{O}_2\text{(g)} \rightarrow \text{H}_2\text{O(l)}\) | \(\Delta H_3\) |

Which of the following mathematical expressions correctly determines \(\Delta H^\circ_{rxn}\) for the dehydrogenation reaction?

- **A.** \(\Delta H^\circ_{rxn} = \Delta H_1 - \Delta H_2 - \Delta H_3\)
- **B.** \(\Delta H^\circ_{rxn} = \Delta H_1 + \Delta H_2 + \Delta H_3\)
- **C.** \(\Delta H^\circ_{rxn} = \Delta H_1 - \Delta H_2 + \Delta H_3\)
- **D.** \(\Delta H^\circ_{rxn} = -\Delta H_1 + \Delta H_2 + \Delta H_3\)

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/119248/*