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The heats of formation of CO(2(g)) , H2O...

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. 

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`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).`
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