Energy Changes

• Exothermic reaction

  Transfers energy to the surroundings usually by heating
• Exothermic reactions

  • Combustion
  • Neutralisation
• Endothermic reaction

  Takes in energy from the surroundings (fall in temperature)
• Endothermic reactions


  • Thermal decomposition
• Uses of exothermic reactions


  • Hand warmers
  • Self heating cans
• Uses of endothermic reactions


  • Sports injury packs
• Reaction profile


  Shows relative energies of the reactants and products in a reaction and how energy changes over the course of a reaction
• Activation energy (Ea)

  The minimum energy required for a reaction to occur
• Required practical


  1. Measure 50 cm3 of hydrochloric acid into a polystyrene cup

  2. Measure the temperature of the hydrochloric acid

  3. Add one spatula of magnesium powder to the hydrochloric acid and stir. Put on the lid

  4. Measure the highest temperature the mixture reaches

  5. When the temperature no longer changes, record the temperature
• Reaction Profiles

  A) exo

  B) endo