Le Chatelier’s Principle

Ammonia is manufactured through the Haber Process.

An industrial plant uses a temperature of 450°C, a pressure of 200 atmospheres and an iron catalyst. Evaluate these conditions in the Haber process.

[6 marks]

Visual Mark Scheme Breakdown

• What do we know about reaction to make ammonia?

  • Forward reaction to make ammonia is Exothermic

  • Forward reaction to make ammonia has less moles (2) whilst the reverse has more moles (4)

• How can we use Le Chatelier's principle to make more ammonia?

  • LOW Temperature shifts the position of equilibrium towards Exothermic direction so it can warm back up

  • So LOW temperature = more ammonia produced

  (1 mark)

• Why don't we make the temperature very low?

  • We need high temperature to increase rate of reaction as heat increases kinetic energy of particles and frequency of successful collisions.

  • An iron catalyst can help increase rate of reaction too.

  • So we can use 450 degrees celsius as a compromise

  (2 mark)

• How can we use Le Chatelier's Principle for Pressure to make more ammonia?

  • HIGH pressure shifts the position of equilibrium towards side with less moles.

  • The right side has 2 moles and the left has 4, so:

  • HIGH pressure = more ammonia produced

  (1 mark)

• Why don't we make the pressure very high?

  • High pressure increases cost and risk of hazards

  • So we can use 200 atmospheres as a compromise

  (2 marks)