When $6 \cdot 0 \mathrm{~g}$ of graphite reacts with dihydrogen to give methane gas, $37 \cdot 4…
When $6 \cdot 0 \mathrm{~g}$ of graphite reacts with dihydrogen to give methane gas, $37 \cdot 4 \mathrm{~kJ}$ of heat is liberated. What is standard enthalpy of formation of $\mathrm{CH}_{4_{(g)}}$ ?
$112 \cdot 2 \mathrm{~kJ} \mathrm{~mol} \cdot 1$
$-74 \cdot 8 \mathrm{~kJ} \mathrm{~mol}^{-1}$
$-37 \cdot 4 \mathrm{~kJ} \mathrm{~mol}^{-1}$
$-112 \cdot 2 \mathrm{~kJ} \mathrm{~mol}^{-1}$
Solution
$\mathrm{C}_{(8)}+2 \mathrm{H}_{2(8)} \longrightarrow \mathrm{CH}_{4(\mathrm{~g})}$
For $6.0 \mathrm{~g}$ of graphite, $\Delta \mathrm{H}=-37.4 \mathrm{~kJ}$
$\therefore$ For $12.0 \mathrm{~g}$ of graphite, $\quad \Delta \mathrm{H}^{0}=\frac{-37.4 \times 12}{6}=-74.8 \mathrm{~kJ} \mathrm{~mol}^{-1}$