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 beA. `+1412 kJ mol^(-1)`B. `-1412 kJ mol^(-1)`C. `+141.2 kJ mol^(-1)`D. `141.2 kJ mol^(-1)`

Answer» Correct Answer - B
`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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