Determine enthalpy change for,
`C_(3)H_(8(g))+H_(2(g))rarr C_(2)H_(6(g))+CH_(4(g))`
at `25^(@)C` using heat of combustion values under standard condition.
`{:(Compounds,H_(2(g)),CH_(4(g)),C_(2)H_(6(g)),C_((Graph ite))),(DeltaH^(@)i n kJ//mol,-285.8,-890.0,-1560.0,-393.5):}`
The standard heat of formation of `C_(3)H_(8(g))` is `-103.8 kJ mol^(-1)`.

Answer

`-55.7kJ`

Explanation

`H_(2)(g)+(1)/(2)O_(2)(g)toH_(2)O,(DeltaH=-285.8kJ)` . . .(i)
`CH_(4)(g)+2O_(2)(g)toCO_(2)(g)+2H_(2)O,(DeltaH=-890.0kj)` . . .(ii)
`C_(2)H_(6)(g)+(7)/(2)O_(2)(g)to2CO_(2)(g)+3H_(2)O,(DeltaH=-1560.0kJ)` . . .(iii)
`C+O_(2)(g)toCO_(2)(g)," "DeltaH=-393.5kJ)` . . .(iv)
`3C+4H_(2)(g)toC_(3)H_(8)(g)," "(DeltaH=-103.8kJ)` . . .(v)
Multiplying eq. (i) by 5 and eq. (iv) by 3 and adding both the equation and subtracting eqs. (ii), (iii) and (v).