Calorimetry

KEY POINTS:

• The amount of energy released during exothermic reactions can be measured by calorimetry.
• One calorie is the amount of energy required to raise the temperature of 1g or water by 1 degree centigrade (or 1 degree Kelvin). This is equal to 4.18 Joules.
• It just so happens the specific heat capacity of water is 4.18 Joules. (What a coincidence!) If we measure the temperature rise in the surrounding water during an exothermic reaction we can then calculate the enthalpy change.
  Quantity of energy released = mass of water x temperature rise x 4.18
• If the reaction is the burning of a fuel, water in a copper or aluminium pot is placed directly above the flame, heated and temperature change measured.
• If the reaction is occurring in aqueous solutions, the experiment is performed in a polystyrene cup and the temperature change of the reaction mixture observed.
• To determine the actual enthalpy change, we need to divide the quantity of energy released by the number of moles of limiting reagent.