Energy Changes

• the amount of energy at the end of a chemical reaction is the same as before the reaction took place
• when energy is transferred to the surroundings:

  • the products will have less energy than the reactants
• an exothermic reaction is a reaction where energy is transferred to the surroundings, so the temperature of the surroundings increases
• endothermic reaction is a reaction that takes in energy from its surroundings, so the temperature of the surroundings decreases
• Examples of exothermic reactions:

  • oxidation
  • combustion
  • neutralisation
• Examples of endothermic reactions:

  • thermal decompostion
  • photosynthesis
• exothermic reactions are used in:

  • self heating cans
  • hand warmers
• endothermic reactions are used in sports injury packs
• chemical reactions can only occur when reacting particles collide with each other with sufficient energy
• activation energy is the the minimum amount of energy needed to start a chemical reaction
• reaction profiles show:

  • relative energies of reactants and products
  • the overall energy change of a reaction
  • the activation energy
• During a chemical reaction, energy is either released or absorbed.
• bond energies is:

  • the energy released when bonds are formed
  • the energy needed to break bonds