Energy changes in reactions

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  • Energy changes (in reactions)
    • Two types of energy changes in reactions
      • EXOTHERMIC (energy given out)
        • Examples
          • The combustion of fuels
          • The neutralisation of an acid by an alkali
          • The reaction between iron and sulfur
          • The reaction between hydrochloric acid and magnesium
        • ?System loses energy
        • ?The temperature of the surroundings increases
        • Is the energy more or less than the energy given out?
          • ENDOTHERMIC (energy taken in)
            • Examples
              • Photosynthesis (uses energy from sunlight)
              • The thermal decomposition of calcium carbonate
              • Reactions that take place during cooking
              • The reaction between sodium hydrogen carbonate (baking soda) and citric acid
            • ?The temperature of the surroundings decreases
            • System gains energy 
          • more
            • Then the reaction absorbs energy, overall. So its an ENDOTHERMIC reaction
          • less
            • Then the reaction releases energy, overall. So its an EXOTHERMIC reaction
      • ENDOTHERMIC (energy taken in)
        • Examples
          • Photosynthesis (uses energy from sunlight)
          • The thermal decomposition of calcium carbonate
          • Reactions that take place during cooking
          • The reaction between sodium hydrogen carbonate (baking soda) and citric acid
        • ?The temperature of the surroundings decreases
        • System gains energy 
    • 10J of energy   in the reactant                                                                                       6J of energy in the product
      • Why?
        • 2J are used for breaking bonds & 2J of energy are used for making new bonds
          • Overall energy change = breaking of bonds & making of new bonds

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