GCSE Combined Science (AQA)

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Conservation of Energy

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Energy changes Exothermic and endothermic reactions

Conservation of Energy

2:57 Types of Chemical Reaction
Spec 4.5.1.1
Previous Energy & State Changes Next Exothermic Reactions
  • All chemical reactions involve a transfer of energy.
  • Example: Explosive reaction by adding a group one metal to water.
  • Energy is transferred to the surroundings, releasing light, heat, and sound energy.
  • Energy is conserved in chemical reactions, meaning it is maintained or kept the same.
  • Energy cannot be created or destroyed; the amount of energy in the universe remains the same before and after a chemical reaction.
  • Energy starts as chemical energy in reactants, such as a group one metal and water.
  • During chemical reactions, energy is transferred between molecules and the surroundings.
  • Example: Wood fire, scientifically known as fuel undergoing combustion.
  • Chemical energy in reactants is transferred to other forms, primarily heat energy.
  • If a reaction transfers energy to the surroundings, product molecules have less energy than reactants.
  • Example: Combustion of wood with reactants initially containing 100 kilojoules of energy.
  • Reaction transfers energy to surroundings as light and heat, resulting in products with less energy.
  • The difference in energy is equal to the amount transferred to the surroundings.
  • Example: Starting with 100 kilojoules and ending with 20 kilojoules, the difference is 80 kilojoules transferred to the surroundings.

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