Exothermic and endothermic (+bond energies)

• When chemical reactions occur, energy is conserved. Energy is not created or destroyed.
• If a reactions transfers energy to its surroundings, the product molecules must have less energy than the reactions
• Exothermic reactions transfer energy to the surroundings, causing the temperature of the surroundings to increase
• Examples of exothermic reactions:

  • combustion
  • neutralisation
• Real life examples of exothermic reactions:

  • self heating cans
  • hand warmers
• Endothermic reactions take in energy form the surroundings, causing the temperature of the surroundings to decrease
• Examples of endothermic reactions:

  • thermal decomposition
  • citric acid and sodium hydrogen carbonate
• Real life examples of endothermic reactions:

  • sports injury packs
• chemical reactions can only occur when reacting particles collide with eachother with sufficient energy
• Activation energy is the minimum amount of energy particles must have to react
• During a chemical reaction, energy must be supplied to break bonds in reactants. energy is released when bonds in the product are formed.
• SUM OF ENERGY TAKEN TO BREAK BONDS - SUM OF ENERGY RELEASED TO FORM BONDS = OVERALL ENERGY CHANGE
• Required Practical 4 ( do the diagram first)

  A) thermometer

  B) beaker

  C) 30

  D) hydrochloric

  E) thermometer

  F) 5

  G) hydroxide

  H) thermometer

  I) temperature

  J) 5

  K) 40

  L) trial