Question

The heat liberated when 1.89 g of benzoic acid is burnt in a bomb calorimeterat`25^(@)C`increases the temperature of`18.94kg`of water by `0.632^(@)C`. If the specific heat of water at`25^(@)C` is 0.998cal`// g// deg`, the value of heat of combustion of benzoic acid is
A. `881.1kcal`
B. `771.4 kcal`
C. `981.1kcal`
D. `871.2kcal`

Answer 1

Correct Answer - B
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`.