The heats of formation of CO_(2(g)) , H_2O_((l)) and CH_(4(g)) are respectively –394 kJ mol^(-1), -286 kJ mol^(-1) and -76 kJ mol^(-1). Calculate the heat of combustion of methane.

The heats of formation of CO_(2(g)) , H_2O_((l)) and CH_(4(g)) are res

1.	The heats of formation of CO_(2(g)) , H_2O_((l)) and CH_(4(g)) are respectively –394 kJ mol^(-1), -286 kJ mol^(-1) and -76 kJ mol^(-1). Calculate the heat of combustion of methane.
Answer» Solution :`C _("graphite") + O _(2 (G)) to CO _(2 (g)) , DELTA H _(1) =- 394 kJ` `H _(2 (s)) + (1)/(2) O _(2 (s)) to H _(2) O _((l)) , Delta H _(2) =- 286 kJ` `C _("graphite") + 2H _(2 (g)) to CH _(4(g)) , Delta H _(4 (g)) , Delta H _(3) =- 76 kJ` The requird equation is, `CH _(4 (g)) + 2O _(2 (*g)) to CO _(2 (g)) + 2H _(2) O _((l)) : Delta H =?` `Delta H = Delta H _(1) + 2 Delta H _(2) - Delta H _(3) =- 394+ 2 (-286) - (-76)` The heat of combustion of methane `= - 890 kJ mol^(-1).`