$H_2O _{(g)} + C_{(s)} = CO_{(g)} + H_{2{(g)}}$; $\Delta H = 131\, KJ$, $CO_{(g)} + \frac{1}{2}\,O_{2{(g)}} = CO_2$$_{(g)}$ ; $\Delta H = -282\, KJ,H_2$ $_{(g)}$$+ \frac{1}{2}\,O_2$$_{(g)}$ $= H_2O$$_{(g)}$; $\Delta H = - 242\, KJ, $ $C_{(s)}$ $+ O_2$ $_{(g)}$ $= $ $ CO_2$ $_{(g)}$; $\Delta$ $H = - x\,\,KJ$
હેસના નિયમ અનુસાર ; \( (iv) = (i) + (ii) + (iii)\)
\(-X = +131 - 282 - 242 X = 393\, kJ\)