The heat liberated when 1.89 g of benzoic acid is burnt in a bomb calorimeter at 25 °C increases the temperature 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 (AFMC 2010)

Mass of benzoic acid=1.89g Temperature of bomb calorimeter=298K Mass of water(m)=18.94=18940g Increase in temperature =0.632 Specific heat of water(s)=0.998cal/g-deg Heat gained by water or heat liberated by benzoic acid(Q)= mS T 18940 0.998 0.632 11946.14cal x x Since,1.89g of acid, liberates 11946.14cal of heat. Therefore heat liberated by 122g(mol.wt of benzoic acid) of acid= mS T 18940 0.998 0.632 11946.14cal x x 11946.14 122 771.1kcal 1.89 x