Question

A bomb calorimeter, or a constant volume calorimeter, is a device often used to determine the heat of combustion of fuels and the energy content of foods. In an experiment, a 0.3833 g sample of phenanthrene (C14H10) is burned completely in a bomb calorimeter. The calorimeter is surrounded by 1.284×103 g of water. During the combustion the temperature increases from 22.04 to 24.54 °C. The heat capacity of water is 4.184 J g-1°C-1. The heat capacity of the calorimeter was determined in a previous experiment to be 909.2 J/°C. Assuming that no energy is lost to the surroundings, calculate the molar heat of combustion of phenanthrene based on these data. C14H10(s) + (33/2) O2(g) 5 H2O(l) + 14 CO2(g) + Energy

Solve for Molar Heat of Combustion = kJ/mol

Answer 1

Heat released in reaction = heat absorbed by water + heat absorbed by calorimeter

           = specifi cheat of water x temp change x mass of water +   specific heat of calorimter x temp change

       = ( 4.184 x ( 24.54-22.04) x 1284)   + ( 909.2 x ( 24.54-22.04)

    = 13430.64 + 2273   = 15703 J = 15.7 KJ

Moles of sample = mass/molar mass = 0.3833 /178.23 = 0.00215

Molar heat of conmbustion in KJ/mol = ( 15.7/0.00215) = 7304 KJ/mol