GCSE Chemistry (AQA)

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Energy in Bonds

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Energy changes Exothermic and endothermic reactions

Energy in Bonds

2:58 Bond Energies
Spec 4.5.1.3
Previous Effects of Atmospheric Pollutants Next Bond Energy Calculations
  • Energy must be supplied to break bonds in reactants during a chemical reaction.
  • Example: Reaction between a carbon atom and an oxygen molecule requires breaking bonds between oxygen atoms.
  • Energy is needed to break bonds, similar to pulling apart two magnets.
  • Energy is transferred into the system to break bonds.
  • Energy is released when new bonds are formed in the products.
  • Example: Carbon and oxygen form new bonds to make carbon dioxide, releasing energy.
  • Exothermic reactions release more energy from forming new bonds than is needed to break existing bonds.
  • Exothermic reactions transfer energy to the surroundings.
  • Reaction profile graph shows energy changes during a reaction.
  • Energy needed for bond breaking is less than energy released in bond making in exothermic reactions.
  • Endothermic reactions require more energy to break existing bonds than is released from forming new bonds.
  • Endothermic reactions take in energy from the surroundings.
  • Reaction profile graph for endothermic reactions shows more energy is needed for bond breaking than is released in bond making.

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