5-Energy Changes

• Activation energy


  The minimum amount of energy for particles to collide with in order for a successful reaction to occur
• Alkaline batteries


  Non-rechargeable. In non-rechargeable cells and batteries the chemical reactions stop when one of the reactants has been used up
• Battery


  Batteries consist of two or more cells connected together in series to provide a greater voltage
• Chemical cells


  Cells contain chemicals which react to produce electricity
• Endothermic reaction


  An endothermic reaction is one that takes in energy from the surroundings so the temperature of the surroundings decreases. In an endothermic reaction, the energy needed to break existing bonds is greater than the energy released from forming new bonds
• Exothermic reaction


  An exothermic reaction is one that transfers energy to the surroundings so the temperature of the surroundings increases. In an exothermic reaction, the energy released from forming new bonds is greater than the energy needed to break existing bonds
• Fuel cells


  Fuel cells are supplied by an external source of fuel (eg hydrogen) and oxygen or air. The fuel is oxidised electrochemically within the fuel cell to produce a potential difference
• Overall energy change of the reaction

  The difference between the sum of the energy needed to break bonds in the reactants and the sum of the energy released when bonds in the products are formed
• Reaction profile


  Reaction profiles can be used to show the relative energies of reactants and products, the activation energy and the overall energy change of a reaction
• Rechargeable cells


  Rechargeable cells and batteries can be recharged because the chemical reactions are reversed when an external electrical current is supplied