1.

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 + 160 kJ/mol

Answer»

`- 6.2 KJ`
`- 37.4 kJ`
`- 35.5 kJ`
` - 20.0 kJ`

SOLUTION :`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`.


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