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Calculate the heat of formation of metha...

Calculate the heat of formation of methane in `kcalmol^(-1)` using the following thermo chemical reactions
`C(s)+O_(2)toCO_(2)(g) , DeltaH=-94.2 kcal mol^(-1)`
`H_(2)(g)+1/2O_(2)(g)toH_(2)O(l) , DeltaH=-68.3 kcal mol^(-1)`
`CH_(4)(g)+2O_(2)(g)toCO_(2)(g)+2H_(2)O(l) , DeltaH=-210.8 kcal mol^(-1)`

Text Solution

Verified by Experts

The correct Answer is:
`-20`
`C(s)+O_(2)(g)toCO_(2)(g)+94.2kcal` …..(1)
`H_(2)(g)+1/2O_(2)(g)toH_(2)O(l)+68.3kcal` …(2)
`CH_(4)(g)+2O_(2)(g)toCO_(2)(g)+2H_(2)(l)+210.8 kcal` ….(3)
The required equation is
`C(g)+2H_(2)(g)toCH_(4)(g)`
so, `DeltaH_(f)=DeltaH_(1)+(2xxDeltaH_(2))-DeltaH_(3)=-20kcalmol^(-1)`
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