MCQ
The difference between $\Delta H$ and $\Delta U$ $(\Delta H - \Delta U),$ when the combustion of one mole of heptane $(I)$ is carried out a temperature $T$ is equal to
- ✓$-4\,RT$
- B$-3\,RT$
- C$3\,RT$
- D$4\,RT$
✓
Answer
Correct option: A.
$-4\,RT$
a
${C_7}{H_{16}}(l) + 11{O_2}(g) \to 7C{O_2}(g) + 8{H_2}O(l)$
${C_7}{H_{16}}(l) + 11{O_2}(g) \to 7C{O_2}(g) + 8{H_2}O(l)$
$\Delta {n_g} = {n_p} - {n_r}$
$ = 7 - 11 = - 4$
$\because \,\Delta H = \Delta U + \Delta {n_g}RT$
$\therefore \,\Delta H - \Delta U = - 4\,RT$
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