Exothermic and Endothermic Reactions

Energy is moved around in chemical reactions

• Chemicals store a certain amount of energy, and different chemicals store different amounts
• If the products of a reactions store more energy than the original reactants, then they must have taken in the difference in energy between the products and reactants from the surroundings during the reaction
• But if they store less, then the excess energy was transferred to the surroundings during the reaction

In an exothermic reactions, heat is given out

• An exothermic reaction is one which transfers energy to the surroundings, usually by heating
• The best example of an exothermic reaction is burning fuels, also called combustion
  • This gives out a lot of energy, it’s very exothermic
  • Neutralisation reactions are also exothermic

In an endothermic reaction, heat is taken in

• An endothermic reaction is one which takes in energy from the surroundings, this is shown by a fall in temperature
• They also have everyday uses such as:
  • In some spots injury packs