Energy Changes

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  • Created by: elle2121
  • Created on: 10-09-19 16:41
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  • Energy Changes
    • Exothermic
      • A reaction which transfers energy to the surroundings
        • Temperature increases
        • If products store less energy then reactants
      • Combustion
      • Neutralisation
      • Handwarmers & self heating cans
    • Endothermic
      • A reaction which takes in energy from the surroundings
        • Temperature decrease
        • If products store more energy then reactants
      • Thermal decomposition
      • Citric acid and sodium hydrogencarbonate
      • Sports injury packs
    • Bond Energies
      • Bond breaking is endothermic (takes in energy)
        • Endothermic
          • A reaction which takes in energy from the surroundings
            • Temperature decrease
            • If products store more energy then reactants
          • Thermal decomposition
          • Citric acid and sodium hydrogencarbonate
          • Sports injury packs
      • Bond making is exothermic (releases energy)
        • Exothermic
          • A reaction which transfers energy to the surroundings
            • Temperature increases
            • If products store less energy then reactants
          • Combustion
          • Neutralisation
          • Handwarmers & self heating cans
        • Energy released by forming bonds is greater then energy needed to break bonds
      • Activation energy
        • Minimum amount of energy needed to break bonds & start reaction
      • Overall energy change = energy required to break bonds - energy released to form bonds
    • Cells
      • Electrochemicalcell
        • 2x diff. electrodes in electrolyte (contains ions which react with electrodes)
        • Reactions between electrodes & electrolyte set up charge diff. between electrodes
          • When electrodes connect by a wire, charge flows & electricity produced
      • Batteries
        • Rechargeable
          • Reaction can be reversed when connected to an external electric current
        • Non-rechargeable
          • Reaction at electrodes are irrreverisible
            • When reactants run out reaction cant take place, no electricity
        • 2+ cells, connected in series
          • Battery voltage = voltage of all cells combines
      • Voltage
        • Increasing the difference of electrodes reactivity increases the cells voltage
          • Diff. metals react diff. with same electrolyte
        • The electrolyte used affects voltage size
          • Diff. ions react diff. with electrodes used
    • Fuel Cells
      • Hydrogen Oxygen Fuel Cells
        • Redox
        • Hydrogen looses electrons at the anode producing H+ ions
          • Oxidation
          • H+ ions move to cathode
            • Oxygen gains electrons from the cathode
              • At the cathode oxygen and H+ ions react, producing water
              • Reduction
        • Electrons flow from the anode to the cathode from an external circuit
          • This creates electric current
      • Less polluting
      • Only produce water & heat
      • Better than electrical vehicles batteries
        • Batteries store less energy - charges more often

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