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.

Options

A. `-372 kcal`
B. `162 kcal`
C. `-340 kcal`
D. `183.5 kcal`

Answer

A

Explanation

Aim : `C_(2)H_(6)+7//2O_(2)to2CO_(2)+3H_(2)O`
`Delta_(r)H^(@)=[2xxDelta_(f)H^(@)(CO_(2))+3Delta_(f)H^(@)(H_(2)O)]-[Delta_(f)H^(@)(C_(2)H_(6))+7//2Delta_(f)H^(@)(O_(2))]`
`=2xx(-94.1)+3xx(-68.3)-(-21)`
`=-188.2-204.9+21=372.1 kcal`