INDUSTRIAL PROCESSES. We try to obtain max. efficiency (min. waste, min. input of energy, and as rapid rxn as possible) in these processes. Max efficiency is possible through 2 ways: A-) kinetics ( how fast the products are made from the reactants)
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A-) kinetics ( how fast the products are made from the reactants)
B-)equilibrium (how much of the desired product is obtained)
Ammonia is produced industrially by the Haber process which involves the catalytic reduction of nitrogen by hydrogen at temperatures of 450-500 ºC and pressures of 35-40 MPa.Fe(s) is used as a catalyst for the reaction.
The process provides an excellent illustration of Le Chatelier's Principle, and is a favourite of examiners!
1. Lower temp is needed.
- But it will decrease the rate of the reaction.
- so, a compromise temp is chosen. Take a look at the graph on P. 189.
2. Finely grinded catalyst will increase the rate.
3. High pressure is needed.
- It will be between 200 – 1000atm (20- 100MPa) since the cost is considered.
4. Min amount of waste:Remaining N2 and H2 are recycled.
- 20% of N2 and H2 mixture is converted to ammonia.The remaining N2 and H2 mixture isn’t wasted. The mixture of N2 , H2 , and NH3 are coolled down until all NH3 liquifies. NH3 is separated & N2 and H2 are recycled.
- Excellent conversion is obtained with only about 2 atm which is required to obtain the flow rate of the gases in the reactor.
- However, the temp cannot be too low.Otherwise, the process will be too slow.A compromise temp is chosen: 700-800 K.
Two gases A and B in a container at a constant temperature, T, and pressure, P, reach equilibrium after a time t1 s. They react according to the reaction
A + B C (ΔH < 0)
The diagram shows the change in the concentrations [X] ofA, B and C with time t. What stress is applied at time t = t2 s?
A) [A] is increased at constant P and T
B) T is increased at constant P
C) P is decreased at constant T
D) [B] is decreased at constant P and T
E) [C] is increased at constant P and T
Which set of conditions will optimize the yield of ammonia in the Haber process, which takes place according to the reaction below?
N2(g) + 3H2(g) 2NH3(g) (ΔH < 0)
A) High temperature and low pressure
B) Low temperature and high pressure
C) Low temperature and low pressure
D) High temperature and high pressure
Low temperatures (since ΔH < 0)
and high pressures (since a decrease in volume will occur) will favour the formation of NH3.