1. Calorimetry “heat measuring” Energy changes can be calculated by measuring temperature changes in a calorimetre.

2. Calorimetres At their simplest a polystyrene cup and lid. Polystyrene is an insulator and cuts heat losses to the environment. A thermometre measures heat changes during a reaction.

3. Data is substituted into the formula; Energy = M c CΔTΔT where; M = mass C = specific heat capacity Δt = change in temperature.

4. Mass NB The mass used is not the mass of the solid reactants. It is that of the solution in which the reaction takes place. The mass of a solution can be calculated using the formula; Density = mass / volume. Assume that the solution has the same density as pure water. 1 g/cm 3 at 298 K. Eg; 25 cm 3 will have a mass of 25 x 1 = 25 g

5. Specific heat capacity The energy, in joules, required to raise the temperature of 1g of a substance by 1K. Units J/g/K Alternatively the energy, in kilojoules, required to raise the temperature of 1kg of a substance by 1K. Units kJ/kg/K For water it is 4.2 J/g/K (or 4.2 kJ/kg/K)

6. Eg; To raise 1g of water by 1 o C requires; 4.18 Joules So to make 5g hotter by 1 o C needs; 5 x 4.18 = 20.9 Joules

7. Why are our winters (usually) mild? Our British climate is maritime, and water needs more energy to heat up than does land. So maritime climates are milder than continental.

8. Other substances have very different specific heat capacities. Eg Copper c = 0.385 J/g/K Copper requires a lot less energy to heat up, which explains why it is used for boilers and piping.

9. Change in temperature Δt can be simply calculated by subtracting the highest temperature reached during a reaction from the initial temperature. Δt = T 2 – T 1 But this assumes that all heat is released (or taken up) simultaneously. In practice the temperature change occurs more gradually. Δt is better estimated by monitoring the temperature over a period of time, plotting a graph and extrapolating.

10. Energy change into ΔH To convert the energy change, calculated from m c Δt, into an enthalpy change divide by the number of moles of the reactant that is not in excess. ΔH = mcΔt / n Units; kJ/mol NB Signs! If the temperature rises the reaction is exothermic and ΔH is –ve. If the temperature falls it is endothermic and ΔH is +ve

11. Oxygen enters Sample burnt in combustion chamber Waste gases removed by suction pump through a copper coil. Stirrer evens out water temperature. Water absorbs the heat released. Flame calorimetre

12. Bomb calorimetre Firing leads are used to ignite a sample. The sample burns in pure oxygen at 25atm. An insulated water jacket surrounds the chamber. After each test the machine is calibrated electrically to find the energy required to generate the same Δt.