Question

# The heat liberated when $$1.89$$ g of benzoic acid is burnt in a bomb calorimeter at $$25^o$$C increases the temperature of $$18.94$$ kg water in calorimeter by $$0.632^o$$C. If the specific heat of water at $$25^o$$C is $$0.998$$ cal $$g^{-1}$$ $$deg^{-1}$$, then the value of the heat of combustion of benzoic acid is:

A
881.1 kcal
B
771.12 kcal
C
981.1 kcal
D
871.2 kcal

Solution

## The correct option is B $$771.12$$ kcalMass of benzoic acid, $$m=1.89$$ g$$T=25^0C$$Mass of water,$$m_{H_2O}=18.94\ kg=18940\ g$$$$\Delta T=0.632^0C$$specific heat of water, $$C_V=0.998 cal/g$$heat gained by water,$$q=mC\Delta T$$$$q=18940 \times 0.998 \times 0.632$$$$q=11946.14\ cal$$Heat released by the caloriemeter= heat gained by waterthus heat released by 1.89 g of benzoic acid = $$11946.14$$ calsince heat of combustion=heat released by 1 mol of benzoic acidthus heat released by $$1$$ mol or $$122$$ g of benzoic acid$$\frac{11946.14}{1.89} \times 122$$$$=771126.5cal=771.12 kcal$$ heat is liberated from combustion of benzoic acidChemistry

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