Chemical Reactions in Solution (Oxford AQA IGCSE Combined Science Double Award) : Revision Note

Calculating Energy Changes for Reactions in Solution

• To calculate the amount of energy produced by a chemical reaction in solution we measure the temperature change when the solutions are mixed together

• The solutions need to be mixed together in an insulated contain to prevent heat loss

• This method can be used for:

  • Neutralisation reactions

  • The reactions of solids with water

Equipment Set up

• Method:

  1. A fixed volume of one reagent is added to the calorimeter and the initial temperature taken with a thermometer

  2. An excess amount of the second reagent is added and the solution is stirred continuously

  3. The maximum temperature is recorded and the temperature rise calculated

• Again, the energy released would be calculated using:

  Q = m x c x ΔT

  • Q = the heat energy change, J

  • m = the mass of the substance being heated, g

  • c = the specific heat capacity, J/g/°C

  • ΔT = the temperature change, °C

• We assume that the density of the solution is the same as pure water, i.e. 1 g/cm³