1.

The standard molar heat of formation ethane, CO_(2) and water (l) are respectively -21.1, -94.1 and -68.3 kcal. The standard molar heat of combustion of ethane will be

Answer»

`-372 kcal`
162 kcal
`240` kcal
183.5 kcal

Solution :Given,
(i) `2C+3H_(2)toC_(2)H_(6),DeltaH=-21.1` kcal
(II) `C+O_(2) to CO_(2),DeltaH=-94.1kcal`
(iii) `H_(2)+(1)/(2)O_(2) to H_(2)O,DeltaH=-68.3kcal`
MULTIPLYING Eq. (ii) by 2 and eq. (ii) by 3 then follow, 2(ii)+3
(iii)-(i)
`C_(2)H_(6)+(3)/(2)O_(2) to 2CO_(2)+3H_(2)O`
`Deltax=2(-94.1)+3(-68.3)-(-21.1)`
`=372` kcal


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