Naphthalene combustion can be used to calibrate the heat capacity of a bomb calorimeter. The heat of combustion of naphthalene is ±40.1 kJ/g. (continued in description)

Question

When 3.450 g of naphthalene was burned in a calorimeter

containing 1.000 kg of water, a temperature rise of 4.345°C was observed. What is the heat

capacity of the bomb calorimeter (excluding the water)?

Answer 1

Heat generated by combustion of 3.450 g naphthalene:

3.450 g x 40.1 kJ / g = 138 kJ

This heat will be absorbed by both the water and the calorimeter to raise the temperature of both.

q = mC∆T + C_cal∆T

q = heat = 138 kJ

m = mass of water = 1.000 kg

C = specific heat of water = 4.184 kJ/kgº

∆T = change in temperature = 4.345º

C_cal = calorimeter constant

Solve the equation for C_cal...

138 kJ = (1.000 kg)(4.184 kJ/kgº)(4.345º) + (C_cal)(4.345º)

138 kJ = 18.18 + 4.345C_cal

C_cal = 27.6 kJ/º