Energy changes

• exothermic reactions

  • to the surroundings
  • combustion
  • neutralisation
  • oxidation
• endothermic reactions

  • energy taken in from the surroundings
  • thermal decomposition
  • citric acid and sodium hydrogen carbonate
• exothermic reaction uses

  • hand warmers
  • (disposable) use energy released by iron oxidation
  • (reusable) use energy from crystallisation
• endothermic reaction uses

  • sports injury packs
  • ammonium nitrate and water mix creating instant cooling
• Activation energy is the minimum amount of energy that reacting particles must have for a reaction to occur.
• Reaction profiles

  
• Catalysts can increase reaction rates by lowering the activation energy, which increases the likelihood of successful collisions.
• chemical bonds- exothermic

  • energy released by forming > energy required to break bonds
  • overall energy change < 0
• chemical bonds- endothermic

  • energy released by forming < energy required to break bonds
  • overall energy change > 0
• A reaction is exothermic if the total energy released by forming bonds is more than total energy required to break bonds.