Explaining the Haber Process
- The Haber Process produces ammonia from nitrogen and hydrogen:
N2 (g) + 3H2 (g) ⇌ 2NH3 (g)
- The conditions used are:
- a pressure of 200 atmosphere
- a temperature of 450 oC
- an iron catalyst
- These conditions produce an equilibrium yield of ammonia of about 30% which seems low, however it is a balance between achieving a good yield of ammonia in a reasonable amount of time
Explaining the Conditions
- Pressure
- A pressure of 200 atmosphere is used as a compromise
- High pressures would shift the equilibrium to the right due to there being less molecules on the right hand side of the equation resulting in a higher yield
- Very high pressures are hazardous and expensive so a lower pressure is used to reduce the risk
- Temperature
- A temperature of 450oC is used as a compromise
- The forward reaction is exothermic so a low temperature would shift the equilibrium to the right increasing the yield of ammonia
- Low temperatures, however, result in a slower rate of reaction
- The higher temperature allows ammonia to be made within a reasonable time frame
The equilibrirum yield of ammonia at different pressures and temperatures
- Sometimes, there are a multiple methods for producing the same substance
- In cases like this, manufacturers have to consider the raw materials used and the amount of energy required for the process
Examiner Tip
Remember to justify the actual conditions for the Haber process based on cost, yield and reaction rate. The ideal conditions for rate are not the same as the ideal conditions for yield or cost, so compromise is needed.
When considering the raw materials needed for a product, think about whether they are renewable or non renewable.
