Reversible reactions

2.4 Energy changes

undefined Acid, bases and salts

Reversible reactions

  1. Equilibrium

    1. For reversible reaction in a closed system, equilibrium is reached when the reactions occur at exactly the same rate in both directions
    2. The relative amounts of the substances in the reaction at equilibrium depends on the conditions of the reaction
    3. An increase in temperature favours the endothermic reaction and a decrease in temperature favours the exothermic reaction
    4. In gaseous reactions, an increase in pressure favours the reaction that produces the fewer number of molecules, and a decrease in pressure favours the reaction that produces the greater number of molecules
    5. These factors, along with reaction rates, are important when determining the optimum conditions in industrial processes such as the Haber process

  2. The Haber process

    1. Raw materials

      1. The raw materials for the Haber process are nitrogen and hydrogen
      2. Nitrogen is obtained from the air
      3. Hydrogen can be obtained from natural gas or other sources

    2. Process

      1. The purified gases are passed over a catalyst of iron at a high temperature of about 450 °C and a high pressure of about 200 atmospheres
      2. Some of the hydrogen and nitrogen react to form ammonia: N2 (g) + 3H2 (g) ⇌ 2NH3 (g)
      3. The reaction is reversible so some ammonia breaks down again into nitrogen and hydrogen
      4. The produced ammonia is cooled so it liquifies, and is removed
      5. The remaining nitrogen and hydrogen is recycled