Chemistry C3.3

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  • Chemistry C3.3
    • Comparing the energy released by fuels
      • When fuels and food react with oxygen, energy is released in an exothermic reaction
      • A calorimeter can be used to compare the energy released by different fuels or food in a school lab
    • Energy transfers in solutions
      • Can calculate the energy change for reactions in solution by measuring the temperature change
        • Q=mc?T
          • Q= amount of energy transferred to the water
          • M= mass of water
          • C= specific heat capacity of water
          • ?T= temperature change
      • Neutralisation and displacement reactions are both examples of reactions that we can use this technique for
    • Energy level diagrams
      • We can show the relative difference in the energy of reactants and products on energy level diagrams
      • Catalysts provide a pathway with a lower activation energy so the rate of reaction increases
      • Bond breaking is endothermic
      • Bond making is exothermic
    • Calculations using bond energies
      • In an exothermic reaction, the energy released when new bonds are formed is greater than the energy absorbed when bonds are broken
      • In an endothermic reaction, the energy released when new bonds are formed is less than the energy absorbed when bonds are broken
      • We can calculate the overall energy change in a chemical reaction using bond energies
    • Fuel issues
      • Much of the world relies on fossil fuels
      • Fossil fuels are non renewable and cause pollution
      • Alternative fuels need to be found soon
      • Hydrogen is one alternative
        • It can be burned in combustion engines or used in fuel cells to power vehicles

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