Topic C5

• Exothermic:

  • heat is given out
  • transfers energy to the surroundings
  • like combustion
  • Neutralisation and Oxidisation reactions are exothermic
  • Everyday uses such as hand warmers, self heating beverages
• Endothermic:

  • Heat is taken in
  • take energy from the environment, cools it down
  • e.g. reaction between Citric acid and sodium hydrogencarbonate
  • everyday uses like sports injury packs
• Energy transfer can be measured

  • First, insulate a polystyrene cup using a lid and cotton wool
  • measure the temp of your reactants, And put them each into a water bath Set to a temperature so you know they are the
  • react them together, and record the change in temperature
• Reaction profiles show energy changes

  • exothermic and endothermic reaction times are opposite
  • Endothermic Starts with an increase of energy
  • Exothermic ends with an increase of energy
• Bond energies:

  • During a chemical reaction old bonds are broken and new bonds are formed
  • Energy must be supplied to break existing bonds-so its an endothermic process
  • Energy Must be released when new bonds are formed - Its an exothermic process
• Bond energy calculations _ ask ar. make