The Haber Process
3H2(g) + N2(g) ⇌ 2NH3(g)
- The nitrogen is gathered from the air and the hydrogen is gathered from natural gas. (1:3 ratio)
Ammonia has a lower melting point than hydrogen or nitrogen, so it can be separated by condensing off as a liquid. (Collected by liquefying)
Only about 15% of ammonia is actually made from this process, so hydrogen and nitrogen are recycled and go around again to create more ammonia.
- 450 degrees Celsius
- 200 atm
- Iron Catalyst
- Since the reaction is exothermic, the lower the temperature, the higher the yield.
- Low temperatures would make the reaction too slow, so a compromise temperature is used.
- As there are 4:2 ratio of moles, high pressures shift equilibria to the right in order to make more ammonia.
- However, this is expensive to build and maintain the plant, so a compromise pressure is used.
- An iron catalyst is used to lower the activation energy of the reaction and therefore increase the rate at which equilibrium is reached.
- But this does not alter the position of equilibrium, it increases the rate of the production of products and reactants equally.
The Manufacture of Ethanol
CH2=CH2(g) + H2O ⇌ CH3Ch2OH(g)
- Ethanol is manufactured by hydrating ethane with steam, then by distilling the products using fractional distillation.
- Ethanol has a lower melting point than ethene, but ethene also condenses whilst manufacturing, so fractional distillation needs to take place to collect the ethanol.
- A very small amount is actually converted into ethanol (about 5%), so unreacted ethene is recycled.
- 300 degrees Celsius
- 70 atm
- Phosphoric (v) acid catalyst
- The reaction is exothermic.
- If the temperature is lowered, more ethanol is produced because the system tries to oppose the change by increasing the temperature, therefore equilibrium shifts to the right.
- A compromise temperature is used because too low temperatures make the rate of reaction too slow to be cost-effective.
- There is a 2:1 ratio of moles.
- An increase in pressure means an increase in ethanol yield.
- The system tries to oppose the change by reducing the pressure, so equilibrium shifts to the side with fewer moles to try and reduce the pressure, therefore creating more ethanol.
- Phosphoric (V) acid is used.
- It is supported by a solid silicon dioxide, which is washed away with water, making it useless.
- Due to this property, an excess of ethene is used instead of an excess of water (because steam would be cheaper).
That's the end of the topic!
Drafted by Bonnie (Chemistry)