In this problem, the heat energy that is absorbed by the water and the bomb calorimeter is equal to the heat energy that is produced by the combustion by the ethane. Use the following equation to calculate the amount if heat energy.
Q = mass * heat capacity * (Tf – Ti)
Q = 500 * 4.18 * (22.76 – 20.00) = 5,768.4 J
Let’s use a similar equation for the bomb calorimeter.
Q = 420 * (22.76 – 20.00) = 1,159.2 J
Total = 5,768.4 + 1,159.2 = 6,927.6 J
This is the amount of heat energy that is produced by the combustion of 0.005 mole of ethane.
Heat of combustion = 6,927.6 ÷ 0.005 = 1,385,520 J/mol or 1,385.52 kJ/mol
This number rounds to 1,386 kJ/mol. This may be the correct answer, but I believe that there is a mistake in this problem. According to a table in physics book, the heat capacity of iron is 448 J/(kg * ˚C). The bomb calorimeter in my physics room is made of iron. The unit of heat capacity is not J/°C.