Calculate the heat produced when `3.785 L` of octabe reacts with oxygeb to form carbon mono oxide and water vapour at `25^(@)C`. (Density of octane is `0.75025 g mL^(-1)). Delta_(comb)H^(Theta)(C_(8)H_(18)) =- 1302.7 kcal, Delta_(f)H^(Theta) (CO_(2)) =- 94.05 kcal, Delta_(f)H^(Theta) (H_(2)O) =- 64.32 kcal, Delta_(f)H^(Theta) (CO) =- 26.41 kcal mo^(-1)`

Explanation

Number of moles of octane `=(3785 xx 0.7025)/(114.2) = 23.38`
`C_(8)H_(18) +(17)/(2)O_(2) rarr 8CO +9H_(2)O DeltaH = ?`
`C_(8)H_(18) +(25)/(2)O_(2) rarr 8CO_(2) +9H_(2)O DeltaH =- 1302.7 kcal` ..(i)
For equation (i)
`DeltaH = 8 Delta_(f)H (CO_(2)) +9Delta_(f)H(H_(2)O) -Delta_(f)H(C_(8)H_(18))`
`Delta_(f)H^(Theta) (C_(8)H_(18)) = 1302.7 +8 (-94.05) +9(-68.32)`
`=- 64.6 kcal`
`DeltaH = 8 Delta_(f)H^(Theta) (CO) +9Delta_(f)H^(Theta) (H_(2)O) -Delta_(f)H^(Theta) (C_(8)H_(18))`
`=- 761.56`
`DeltaH` for `23.38 mol`
`=- 761.56 xx 23.8 =- 17729 kcal`