Solutions to Web Experiment: Bomb Calorimetry

Web Experiment: Bomb Calorimetry
Answers to Second Set of Questions

1. The heat produced by the combustion of 2.000 g of naphthalene is absorbed by the bucket, the water in the bucket, and the hardware (bomb, fuse wires, stirrer, thermometer). If we measure the amount heat absorbed by the bucket, the water in the bucket, and the hardware (bomb, fuse wires, stirrer, thermometer), then we will know the amount heat released when 2.000 g of naphthalene are burned at constant volume. The volume of the bomb in which the reaction occurs does not change.

2. If the combustion of 2.000 g (1.560 • 10-2 mole) of naphthalene at constant volume produces 80.4 kJ of heat, then the combustion of 128.17 g (1.000 mole) of naphthalene at constant volume will produce 5.15 • 103 kJ of heat. Since the products are not in their standard states at the end of the combustion reaction, - 5.15 • 103 kJ is NOT equal to Dcomb. The additional change in energy required to take the products from their current states to their standard states is approximately 0.1% of DEcomb. The magnitude of this change is comparable to the magnitude of the uncertainty in our measurements and will be neglected in these calculations.

3. The heat of combustion at constant pressure, Dcomb, of one mole of naphthalene is equal to the heat combustion at constant volume, Dcomb, plus the PV work.

4. The standard enthalpy of reaction is the sum of the standard enthalpies of formation of the products (S(nDf (product) )) minus the sum of of the standard enthalpies of formation of the reactants (S(nDf (reactant) ) ).