Question

In order to calibrate a constant volume bomb calorimeter, the combustion of (7.450x10^-1) g of benzoic acid, C₆H₅COOH, was observed to cause the temperature in the calorimeter to rise from 25.000 to (2.87000x10^1) ^oC. The energy of combustion of benzoic acid, ΔU, is -3226.7 kJ mol^-1. What is total heat capacity (C) of the calorimeter (including all its contents) in kJ ^oC^-1?

Answer 1

Molar mass of benzoic acid is 122.12 g/mol

The energy of combustion of benzoic acid, ΔU, is -3226.7 kJ mol^-1 x (122.12 g/mol) = 394x10³ kJ/g

for 1 g of benzoic acid the heat evolved is 394x10³ kJ

for 0.7450 g of benzoic acid the heat evolved is 0.7450 x 394x10³ kJ = 293530 kJ

So this amount is utilized to raise the temperature of the solution in the calorimeter.

So 293530 kJ =  total heat capacity x change in temperature

=  total heat capacity x (28.7 - 25.0 ) oC

total heat capacity = 79332 kJ/oC