1.

If enthalpies of formation of C_(2)H_(4)(g), CO_(2)(g) and H_(2)O(l) at 25^(@)C and 1 atm pressure be 52, - 394 and - 286 kJ mol^(-1) respectively, the enthalpy of combustion of C_(2)H_(4)(g) will be

Answer»

`+1412 kJ mol^(-1)`
`-1412 kJ mol^(-1)`
`+141.2 kJ mol^(-1)`
`141.2 kJ mol^(-1)`

Solution :`C_(2)H_(4)+3O_(2)rarr2CO_(2)+2H_(2)O`
`DeltaH_("reaction")=[2xxDeltaH_(f)^(@)(CO_(2))+2xxDeltaH_(f)^(@)(H_(2)O)]-DeltaH_(f)^(@)(C_(2)H_(4))+3xxDeltaH_(f)^(@)(O_(2))]`
`=[2(-394)+2(-286)]-[52+0]=-1412 kJ`.


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