How much energy is released when 6 mole of octane is burnt in air ? Given `DeltaH_(f)^(@)` for `CO_(2)(g),H_(2)O(g)` and `C_(8)H_(18)(l)` respectively are `-490,-240` and `+160KJ//mol`

Options

A. `- 6.2 kJ`
B. `- 37.4 kJ`
C. `- 35.5 kJ`
D. ` - 20.0 kJ`

Answer

B

Explanation

`C+O_(2)rarrCO_(2) , DeltaH_(F)=-490 kJ//mol - (i)`
`H_(2)+1//2O_(2)rarrH_(2)O, DeltaH_(F)=-240 kJ//mol - (ii)`
`8C+9H_(2)rarrC_(8)H_(18), DeltaH_(F)=+160 kJ//mol - (iii)`
applying
(i)`xx8+(ii)xx9-(iii)`
`C_(8)H_(18)+(25)/(2)O_(2)rarr8CO_(2)+9H_(2)O`
`DeltaH^(@)=-3920-2160-160=-6240 kJ//mol`
`=37440 kJ//mol =-37.4 kJ`.