Exothermic & Endothermic (Edexcel IGCSE Chemistry: Double Science)

• The changes in heat content can be determined and measured with a thermometer
• Note that the overall amount of energy does not change as energy is conserved in reactions
  • This is known as the law of conservation of energy

• This means that it cannot be created or destroyed but it can be transferred
• So, if energy is transferred to the surroundings during a chemical reaction, then the products formed must have less energy than the reactants by the same amount as that transferred

In exothermic reactions, the temperature of the surroundings increases and the heat content of the system falls

In endothermic reactions, the temperature of the surroundings falls and the heat content of the system increases

• The following are some examples of heat changes in reactions
  • Neutralisation reactions:
    • These always give energy out

  • Displacement reactions:
    • These can either take energy in or give it out

  • Combustion reactions:
    • These always give energy out