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Heat changes in chemical reactions
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Heat changes in chemical reactions

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  • 1. HEAT CHANGES IN CHEMICAL REACTIONS
  • 2. The chemical reaction that results in heat produced is called an exothermic reaction.
    Example- Dissolving sodium hydroxide in water.
  • 3. Exothermic reaction accompanied by a rise in temperature of the surrounding.
  • 4. The chemical reaction that absorbs heat from the surrounding is called an endothermic reaction.
    Example- Dissolving ammonium chloride in water.
  • 5. Endothermic reaction resulting a drop of the temperature of the surrounding.
  • 6. Energy graph for an exothermic reaction
  • 7. Energy graph for an endothermic reaction.
  • 8. The change of energy level in a chemical reaction is denoted by the symbol
  • 9. When the energy level of the product is higher than that of reactants , energy is absorbed.
    The reaction is endothermic and is (+) ve.
  • 10. When the energy level of the product is lower than the reactants, energy is released.
    The reaction is exothermic and is (-) ve.
  • 11. HEAT CHANGES IN INDUSTRIAL CHEMICAL REACTION
    If a reaction is exothermic and reversible, heating the process to a very high temperature would decrease the yield of the products.
    Example- Production of ammonia
  • 12. HABER PROCESS
    Production of ammonia
    Nitrogen + Hydrogen Ammonia + Heat
    Heat is given off. So a low temperature will give better yield.
    But a low temperature will cause the reaction to proceed slowly.
    A moderate temperature of 450-500 is used.
  • 13. CONTACT PROCESS
    Production of sulphuric acid.
    Sulphur dioxide + Oxygen Sulphurtrioxide + Heat
    Heat is given off. So a low temperature will give better yield.
    But a low temperature will cause the reaction to proceed slowly.
    A moderate temperature of 400-500 is normally used.
  • 14. The sulphur trioxide is passed into concentrated sulphuric acid to form oleum.
    Sulphur trioxide + Con. Sulphuric acid Oleum
    Oleum + Water Sulphuric acid