C5 - energy changes

• Energy is conserved in chemical reactions. After a reaction, the overall amount of energy in the universe is still the same.
• Endothermic reactions:

  • Take in energy from the surroundings which is shown by the fall in temperature.
  • Thermal decompositions
  • Citric acid + sodium hydrogencarbonate
  • Some sport injury packs
• Exothermic reactions:

  • Transfers energy into the surroundings which is seen in the rise of temperature.
  • Combustion
  • Neutralisation
  • Most oxidation reactions
  • Self heating cans and hand warmers
• Reaction profiles:

  • Activation energy - minimum amount of energy that reactants need to react.

  
• Endothermic reactions - energy used to break bonds is greater than the energy released by forming new bonds.
• Exothermic reactions - energy released by forming bonds is greater than the energy used to break existing bonds.
• overall energy change = total energy energy needed to break bonds - total energy released by forming new bonds