The standard molar heats of formation of ethane, carbon dioxide, and liquid water are `-21.1, -94.1`, and `-68.3kcal`, respectively. Calculate the standard molar heat of combustion of ethane.

Explanation

The required chemical equation for combustion of ethane is
`2C_(2)H_(6)(g)+7O_(2)(g)=4CO_(2)(g)+6H_(2)O(l),DeltaH^(@)=?`
The equation involved 2 moles of `C_(2)H_(6)` heat of combustion of ethane will be `=(DeltaH^(@))/(2)`
`DeltaH^(@)=DeltaH_(f("product"))^(@)-DeltaH_(f("reactants"))^(@)`
`=[4xxDeltaH_(f(CO_(2)))^(@)+6DeltaH_(f(H_(2)O))^(@)]-[2DeltaH_(f(C_(2)H_(6)))^(@)+7DeltaH_(f(O_(2)))^(@)]`
`=[4xx(-94.1)+6xx(-68.3)]-[2xx(-21.1)+7xx0]`
`=-376.4-409.8+42.2`
`=-744.0kcal`
`(DeltaH^(2))/(2)=` Heat fo combustion of ethane `=-(744.0)/(2)=-372.0kcal`