The molar enthalpies of combustion of C_2H_2(g), C (graphite) and… - Vidyadip

MCQ

The molar enthalpies of combustion of $C_2H_2(g), C (graphite)$ and $H_2(g)$ are $-1300, -394,$ and $-286\, KJ \,mol^{-1}$, respectively. The standard enthalpy of formation of $C_2H_2(g)$ is .......$kJ \,mol^{-1}$

✓
$-226 $
B
$-626 $
C
$226$
D
$626$

✓

Answer

Correct option: A.

$-226 $

a
$\mathrm{C}_{2} \mathrm{H}_{2}(\mathrm{g}) +\frac{3}{2} \mathrm{O}_{2}(\mathrm{g}) \longrightarrow 2 \mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O} $

$\Delta {\text{H}} = 2 \times \Delta {{\text{H}}_{\text{C}}} + \Delta {{\text{H}}_{{{\text{H}}_2}{\text{O}}}} - \Delta {{\text{H}}_{{{\text{C}}_2}{H_2}}}$

$=2 \times(-394)+(-286)-(-1300) $

$=+226 \,\mathrm{kJ}\, \mathrm{mol}^{-1} $

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