• 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