.0.50 g of benzoic acid was subjected to combustion in a calorimeter when the temperature of the calorimeter system was found to rise by `0.55^(@)C.` Calculate the enthalpy of combustion of benzoic acid (i) at constant volume (ii) at constant pressure. The thermal capacity of the calorimeter including water was found to be `23.85 kJ K^(-1).`

Explanation

Here, `x = 23. 85 kJ K ^(-1) , Delta T = 0. 55 ""^(@) C, M = 122 g mol ^(-1) , m = 0. 5 g.`
Heat of combustion at constant volume, `q _(v) = z xx Delta T xx M //m`
`= 23. 85 kJ K ^(-1) xx0. 55 K xx 122g mol ^(-1) // 0. 50 g = 3200 . 7 kJ mol ^(-1) =-3200 . 7 kJ mol ^(-1) `