The combustion enthalpy of carbon, hydrogen and methane are -393.… - Vidyadip

MCQ

The combustion enthalpy of carbon, hydrogen and methane are $-393.5 ;\, -284.8$ and $-890.4\, kJ/mole$ respectively at $25\,^oC$ . The value of standard formation enthalpies of methane at that temperature is.....$kJ/mole$

A
$890.4$
B
$-298.8$
✓
$-72.7$
D
$-107.7$

✓

Answer

Correct option: C.

$-72.7$

c
$\mathrm{C}+2 \mathrm{H}_{2} \rightarrow \mathrm{CH}_{4}$

$\Delta \mathrm{H}_{\mathrm{f}}\left(\mathrm{CH}_{4}\right)=\Delta \mathrm{H}^{\mathrm{C}}(\mathrm{C}) \lambda \Delta \mathrm{H}^{\mathrm{C}}\left(\mathrm{H}_{2}\right)-\Delta \mathrm{H}^{\mathrm{C}}\left(\mathrm{CH}_{4}\right)$

$=-393.5+2(-284.8)-(-890.4)$

$=-72.7\, \mathrm{kJ} / \mathrm{mole}$

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