The heat liberated when `1.89 g` of benzoic acid is burnt in a bomb calorimeter at `25^(@)C` increases the temperture of `18.94 kg` of water by `0.632 ^(@)C`. If the specific heat of water at `25^(@)C` is `0.998 cal//g "deg"`, the value of the heat of combustion of benzoic acid is

Options

A. `88.11kcal`
B. `771.4 kcal`
C. `981.1kcal`
D. `871.2kcal`

Answer

B

Explanation

Heat absorbed by water `= m xx s xx Deltat`
`= 18940 g xx 0.998 cal^(-1) g deg^(-1) xx 0.632 ^(@) C`
`=11946.14 cal`
`:. ` Heat produced on combustion of1.89g of benzoic acid`= 11946.14cal`
Molar mass of benzoic acid `( C_(6)H_(5) COOH) = 122g`
`:. `Molar heat of combustion
`= ( 11946.14)/( 1.89) xx 12 cal`
`= 771126.5 cal = 771.12 kcal`.