4.184g of benzoic acid was burnt in bomb calorimeter. The rise in the temperature is `10^@`. The heat capacity of calorimeter and its contents is `2.644 kcal K^(-1)`. Calculate the heat of combustion of benzoic acid. 

Explanation

The heat of combustion= `-((hxx theta xxM))/m`
Rise in temperature of calorimeter and its contents, `theta=10^(@)`
The heat capaciry of calorimeter and its contents,`h=2,644K" cal ^(-1)`
The mass of combustible substance, (benzoic acid), m=4.184g
The molar mass of benzoic acid,=`122g" "mol^(-1)`.
The heat of combustion of benzoic acid = `-(2.644xx4.184xx10xx122)/4.184=-3226KJ" "mol^(-1)=DeltaE`
Since the bomb calorimeter is closed vessel, heat of combustion calculated in it is `DeltaE`
`C_(6)H_(5)COOH_((s)) + 15/2O_(2)(g)to 7CO_(2)(g)+3H_(2)O_((l)), Deltan=7-15/2=-0.5`
Heat of combustion of benzoic acid benzoic acid at constant pressure,
`DeltaH=DeltaE+DeltanRT=-3226-0.5xx8.314xx10^(-3)xx298=(-3227.23KJ)/(mol^(-1))`