Question

The heat of combustion of benzoic acid (C6H5COOH) is -3226 kJ/mol. When 0.841 g of benzoic acid was burned in a bomb calorimeter, the temperature of the calorimeter (including its contents) rose from 23.50 °C to 27.05 °C. What is the heat capacity (calorimeter constant) of the calorimeter?

A.6.25 kJ/°C

B.22.2 kJ/°C

C.79.0 kJ/°C

D.0.439 kJ/°C

E.908 kJ/°C

Answer 1

Given: Heat of combustion of benzoic acid (C₆H₅COOH) is -3226 kJ/mol .i.e.q_v is always positive

.i.e. q_v = 3226  kJ/mol

m = 0.841 g.i.e. of benzoic acid was burned in a bomb calorimeter and

Molar mass of Benzoic acid (M)= 122.12 g/mol

the temperature of the calorimeter (including its contents) rose from 23.50 °C to 27.05 °C .i.e. Q = (27.05 - 23.50)°C = 3.55 °C

q_v = C * Q * (M/m) where C = heat capacity (calorimeter constant) of the calorimeter

q_v = C * Q * (M/m)

3226 KJ/mol = C * 3.55 °C * (122.12 g/mol / 0.841 g)

3226 KJ/mol = C * 515.48 °C/mol

Therefore, heat capacity (calorimeter constant) of the calorimeter.i.e. C = (3226/515.48)KJ/°C = 6.25 KJ/°C

Answer is (A)