Energy Changes

  • Created by: Gaynor
  • Created on: 20-03-18 15:31
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  • Energy Changes
    • Exothermic and Endothermic Reactions
      • An exothermic reaction is a reaction that transfers energy to the surroundings
      • An endothermic reaction is one that takes in energy from the surroundings
      • Hand warmers are exothermic
      • Injury packs are endothermic
      • In an exothermic reaction graph, the products are at a lower level then the reactants
      • In an endothermic reaction graph, the products have a higher energy than the reactants
    • Bond Energies
      • Energy is released when new bonds are formed
        • Bond formation is exothermic
      • Energy must be supplied to break existing bonds
        • Bond breaking is endothermic
      • The overall energy change is the sum of the energies needed to break bonds in the reactants minus the energy released when bonds are formed in the products
    • Cells and Batteries
      • An electrochemical cell is a system made up of two different electrodes in contact with an electrolyte
      • If the electrodes are connected by a wire, a charge is able to flow and electricity is produced
      • Non-rechargeable batteries contain cells which use irreversible reactions. Once one of the reactants is used up, they don't produce any more charge
      • In a rechargeable battery, the reaction can be reversed by connecting it to an external electric current
    • Fuel Cells
      • A fuel cell is an electrical cell that's supplied with fuel and oxygen and uses energy from the reaction between them to produce electrical energy efficiently
      • The electrolyte is often potassium hydroxide
      • Hydrogen goes into the anode compartment and oxygen goes into the cathode compartment
      • Hydrogen ions move to the cathode and oxygen moves to the anode


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