Exothermic and Endothermic Reactions

• Chemicals


  Store a certain amount of energy
• Different chemicals store different amounts of energy
• The products of a reaction store more energy than the reactants


  The products have taken in energy from the surroundings during the reaction
• The products store less energy than the reactants


  The extra energy was transferred (given out) to the surroundings during the reaction
• Energy transferred


  The difference between the energy of the products and the energy of the reactants
• The overall amount of energy doesn't change. This is because energy stays the same (is conserved) in reactions-it can't be made or destroyed, only moved around
• The amount of energy in the universe always stays the same
• Exothermic reaction


  A reaction which gives out energy to the surroundings
• Exothermic reaction


  Shown by a rise in temperature of the surroundings
• Exothermic reactions


  • Burning fuels (combustion)
  • Neutralisation reactions (acid + alkali)
  • Many oxidation reactions
• Exothermic reactions have lots of everyday uses
• Exothermic reaction uses


  • Some hand warmers
  • Self heating cans of hot chocolate and coffee
• Endothermic reaction


  A reaction which takes in energy from the surroundings
• Endothermic reaction


  Shown by a fall in temperature of the surroundings
• Endothermic reactions


  • Reaction between citric acid and sodium hydrogencarbonate
  • Thermal decomposition (when a substance breaks down when it's heated)
• Endothermic reactions also have everyday uses
• Endothermic reaction uses


  • Sports injury packs
• Physical processes can also take in or release energy, e.g. freezing is exothermic, melting is endothermic