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 0.9973 g sample of isophthalic acid (C8H6O4) is burned completely in a bomb calorimeter. The calorimeter is surrounded by 1.319×103 g of water. During the combustion the temperature increases from 25.37 to 28.49 °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 939.3 J/°C. Assuming that no energy is lost to the surroundings, calculate the molar heat of combustion of isophthalic acid based on these data.

Answer 1

find heat released by the burn:

(2 g) (19.4 kJ/g) = 38.8 kJ released

find heat gained by the water:

dH = m C dT

dH = (2250 g) (4.184 J/g-C) (+ 3.17 C)

dH = 29,842 Joules

aka

dH water = + 29.8 kJ

find the missing heat given to the calorimeter

(38.8 kJ released) - (29.8 kJ given to water) = 9.0 kJ given to calorimeter

What is the heat capacity of the empty bomb calorimeter

(9.0 kJ given to calorimeter) / (3.17 C rise in temp) = 2.84 kJ / C