1.

At 300 K, the standard enthalpies of formation of C_(6)H_(5)COOH (s), CO_(2)(g) & H_(2)O (l) are , -408, -393 & -286" kJ mol"^(-1) respectively. Calculate the heat of combustion of benzoic acid at : (i) constant pressure (ii) constant volume.

Answer»


SOLUTION :`C_(6)H_(5)COOH+15/2 O_(2) rarr 7CO_(2)+3H_(2)O(l)`
`DeltaH=(7xx-393)+3(-286)-(408)=-3201`
`DeltaU=DeltaH-Deltan_(g) RT`
`Deltan_(g)=-1/2`
`DeltaU=-3199.75 kJ mol^(-1)`


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