ENDO+EXO

• Exothermic reaction

  A reaction that transfers energy to the surroundings so the temperature of the surroundings increases
• Endothermic reaction

  A reaction that takes in energy from the surroundings so the temperature of the surroundings decreases
• Exothermic reactions


  • Combustion
  • Many oxidisation reactions
  • Neutralisation
• Endothermic reactions


  • Thermal decomposition
  • Reaction of citric acid and sodium hydrogencarbonate
• Everyday examples of exothermic reactions


  • Self-heating cans (e.g. for coffee)
  • Hand warmers
• Everyday examples of endothermic reactions


  • Sports injury packs
• Activation energy


  Minimum amount of energy that particles must have to react
• Reaction profile


  1. Shows the relative energies of reactants and products

  2. Shows the activation energy

  3. Shows the overall energy change of a reaction
• Exothermic reaction


  Products have less energy than reactants
• Endothermic reaction


  Products have more energy than reactants
• Energy changes during a chemical reaction


  1. Energy must be supplied to break bonds in the reactants

  2. Energy is released when bonds in the products are formed
• The sum of energy taken in to break bonds - the sum of energy released to form bonds = the overall energy change
• Endothermic reaction


  Energy taken in to break bonds > energy released when bonds are formed
• Exothermic reaction


  Energy taken in to break bonds < energy released when bonds are formed