$CH_4(g) +2O_2(g) \rightarrow CO_2(g)+2H_2O(l)\,;$ $\Delta H= -890 \,kJ$
$CO_2(g) \rightarrow C($graphite$) + O_2(g) \,;$ $\Delta H= 393 \,kJ$
$2H_2O(l) \rightarrow 2H_2(g) + O_2(g) \,;$ $\Delta H= 571 \,kJ$
$2H_2(g) \rightarrow 4H(g)\, ;$ $\Delta H= 871\, kJ$
$C($graphite$) \rightarrow C(g)\, ;$ $\Delta H= 716\, kJ$
$\Delta \mathrm{H} =-890 \,\mathrm{kJ}$
$\mathrm{CO}_{2}(\mathrm{g}) \longrightarrow \mathrm{C}_{( \text {graphite) } }+\mathrm{O}_{2}(\mathrm{g}) \text { : } $
$\Delta \mathrm{H} =393 \,\mathrm{kJ} $
$2{{\text{H}}_2}{\text{O}}(l) \to 2{{\text{H}}_2}({\text{g}}) + {{\text{O}}_2}({\text{g}}){\text{ : }}$
$\Delta \mathrm{H} =571\, \mathrm{kJ}$
$2 \mathrm{H}_{2}(\mathrm{g}) \longrightarrow 4 \mathrm{H}(\mathrm{g}): \quad \Delta \mathrm{H}=871\, \mathrm{kJ}$
$\mathrm{C}_{(\text {graphite })} \longrightarrow \mathrm{C}(\mathrm{g}) ; \quad \Delta \mathrm{H}=716\, \mathrm{kJ}$
$\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_$
$\mathrm{CH}_{4}(\mathrm{g}) \longrightarrow 4 \mathrm{H}(\mathrm{g})+\mathrm{C}(\mathrm{g}) ; \Delta \mathrm{H}=1661$
$50\, \mathrm{C}-\mathrm{H}=\frac{1661}{4}=415.25$
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