exothermic and endothermic reaction (science)

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  • exeothermic and endothermic reaction
    • Exothermic
      • exothermic reaction is when heat is given out to the surroundings
        • this is shown In rise in temperature
          • for example burning fuel is a great example of exothermic reaction
            • this is also called combustion. this gives out a lot of energy
            • many oxidation reactions are exothermic. for example adding sodium to water releases energy.
              • the reaction releases energy and the sodium moves about on the surface of the water as it oxidised.
      • neutralisation reaction is also exothermic (acid + alkali)
    • Endothermic
      • endothermic is when heat is taken in by the suroundings
        • this is shown by fall in temperature
        • endothermic reactions are much less common than exothermic
          • they include the reaction between citric acid and sodium hydrogencarbonate
            • thermal decomposition e.g. heating calcium carbonate causes it to decompose into calcium oxide (also called quicklime)
              • calcium - CaCOcubed (+heat) - CO2 + CaO = quicklime
            • endothermic reactions are  used in some sports injury packs. the chemical reaction allows the pack to become instantly cooler without having to put it in the freezer.
    • energy transferred can be measured
      • the amount of energy released can be measure by a chemical reaction (in solution) by taking the temperature of the reagents, mixing them in a polystyrene cup and the measuring the temperature of the solution at the end.
        • materials that should be used in the practical: lid, large beaker, polystyrene cup, cotton wool, thermometer and reaction mixture
          • you can reduce the amount of energy loss by putting the polystyrene cup into a beaker of cotton wool to give more insulation of the reactant used.
            • also putting a lid on the beaker reduces energy loss by evaporating.
        • the method works for neutralisation reactions or reactions between metals and acid, or carbonates and acids.
          • this method can also be used to investigate what effect variables  have on the amount of energy transferred. e.g. the mass or concentration of the reactants used.
    • reaction profile
      • reaction profiles are diagrams that show the relative energies of the reactants and products in a reaction, and how the energy changes over the course of the reaction.
        • the initial rise in energy represents the energy needed to start the reaction. this is the activation energy.
          • the activation energy is the minimum amount og energy the reactants need to collide with each other and react
            • the greater the activation energy, the more energy needed to start the reaction. this has to be supplied e.g. by heating the reaction mixture.

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