Chemical Change: Production of Ammonia and Sulfuric Acid

Chemical Change: Production of Ammonia and Sulfuric Acid

Production of Ammonia: The Haber Process

Overview

  • Ammonia (NH₃) is manufactured industrially using the Haber process. The raw materials are nitrogen and hydrogen.
  • Nitrogen is obtained from the air and hydrogen is obtained mainly from natural gas (methane).

The Haber Process

  • The Haber process involves the reaction of nitrogen gas and hydrogen gas to form ammonia. The reaction is reversible.
  • The balanced chemical equation is N₂(g) + 3H₂(g) ⇌ 2NH₃(g).
  • This reaction is carried out at a high pressure (200 to 300 atmospheres) and a moderate temperature (450 °C).
  • A catalyst, usually iron, is used to increase the rate of reaction.
  • The mixture of nitrogen and hydrogen gases recirculates until the equilibrium is reached.

Conditions and Yield

  • Higher pressures favour the forward reaction and increase yield, but the cost and safety concerns limit the practical working pressure.
  • Lower temperatures also favour the forward reaction and increase yield, but they slow down the rate of reaction. Therefore, a compromise temperature is used.

Production of Sulfuric Acid: The Contact Process

Overview

  • Sulfuric acid (H₂SO₄) is produced on an industrial scale using the Contact process. The raw material is sulfur.

The Contact Process

  • The Contact process involves three main steps:
    1. Burning sulfur in air to produce sulfur dioxide (SO₂): S(s) + O₂(g) → SO₂(g).
    2. The sulfur dioxide is then oxidised to sulfur trioxide (SO₃) using a vanadium(V) pentoxide (V₂O₅) catalyst: 2SO₂(g) + O₂(g) ⇌ 2SO₃(g).
    3. Sulfur trioxide is absorbed in concentrated sulfuric acid to give fuming sulfuric acid (oleum), which is then diluted with water to give sulfuric acid: SO₃(g) + H₂SO₄(l) → H₂S₂O₇(l), then H₂S₂O₇(l) + H₂O(l) → 2H₂SO₄(l).

Conditions and Yield

  • Just as with the Haber process, certain conditions affect the yield. The second reaction is exothermic and reversible, so lower temperatures increase the yield but slow the rate of reaction. A compromise temperature is often used.
  • The pressure does not particularly affect the yield so it is carried out at nearly atmospheric pressure for safety and economic reasons.

Remember to regularly revisit these key points to ensure understanding and recall. For a deeper understanding, try to apply these principles to different situations and problems.