There are four molecules of gas on the reactants side (x 1 nitrogen, x3 hydrogen’s).There are two molecules of gas on the products side (x2 ammonia)
The reactant side has a higher pressure because there are more molecules, and thus less space to move.
The product side has lower pressure because there are fewer gas molecules, so more space to move.
Refer to I/GCSE Chemistry, Le Chatelier’s principle states that the product side must do something to counteract the high pressure in the reactant side. So, the product side starts producing more Ammonia by using up the nitrogen and hydrogen in the reactant side. This means that the numbers of hydrogen and nitrogen molecules in the reactant side starts to decrease. When the number of molecules decreases, the pressure also decreases, until it reaches a balanced pressure.
The reaction of Nitrogen and Hydrogen is EXOTHERMIC.
- Favoured by higher pressure and lower temperatures
The decomposition of Ammonia is ENDOTHERMIC
- Favoured by lower pressures and higher temperatures
Le Chatelier’s principle states that if the temperature of the equilibrium reaction rises in the surroundings, it needs to be counteracted by something that takes in energy to lower the temperature.
- Hydrogen + nitrogen reacts and releases energy and forms ammonia = exothermic reaction.
- There is lots of heat energy present in the surroundings. Too much heat/ high temp.--> explosions
- This reaction is counteracted by the ammonia which takes in the energy released from the exothermic reaction.
- Because it takes in the energy, this lowers the temperature of the surroundings, but not too much.
- The ammonia uses the energy to break down to form hydrogen and nitrogen.
Conditions in the industry
When it comes to I/GCSE Chemistry, the conditions for the process are a compromise that balances efficiency with safety + cost.
Higher pressure= higher yield of ammonia
- high pressure plants are expensive to build, thus the pressure is set as high as feasible, at x200 pressures are used.
Low temperatures=higher yield of ammonia
- lower temperature means a slow rate of reaction
You got it now!