Topic 5- Energy changes

• Activation Energy 


  minimum amount of energy reactants particles need in order to collide with each other & react

  
  

  the greater the activation energy the more energy needed to start the reaction - energy has to be supplied
• Exothermic Reactions 


  transfer heat energy to the surroundings

  shown by rise of temp

  e.g combustion reaction, Neutralisation
• Endothermic Reaction


  Absorbs energy from the surrounds

  shown by fall of temp

  e.g. thermal reaction, sport injury packs
• Bond Energy 


  amount of energy required to break one mole of a particular covalent bond

  • Old bonds broken & new bonds formed
• what process is bonds breaking

  endothermic

  • energy must be supplied to break the existing bonds
• what process is bond formation

  Exothermic

  • energy is released when new bonds are formed
• what is energy greater in exothermic reactions

  energy released by forming bonds is greater that energy used to break them
• what is energy greater in endothermic reactions

  energy used to break bonds is greater than energy released by forming them
• factors that affect Voltage in the cell

  BEER

  • B- batteries - lots of them used = bigger volt
  • E- electrode - diff metals react differently to same electrolyte- cause charged difference
  • E- electrolyte - affect size of volt - diff ions in solution will react differently with electrode used
  • R- reactivity -difference in reactivity of electrode= bigger the voltage of cell
• what type of reactions are Non-Rechargeable batteries

  Irreversible reaction

  Once one of the reactants are all used up, cells don't produce any mroe charge & have to replace them

  e.g. alkaline batteries
• what type of reactions are Rechargeable reactions

  Reversible reactions

  The reactions can be reversed by connecting it to external electric charge
• What do Fuel Cells use?

  fuel and oxygen to produce electrical energy
• Process of how Fuel Cells work

  1. fuel enters the cell
  2. it becomes oxidised
  3. so sets a potential difference within the cell
• how are hydrogen-oxygen fuel cells produced?

  hydrogen and oxygen combine to produce clean water & energy