C13: The Production of Ammonia

Question 1

Equilibrium

Answer 1

The point in a reversible reaction when the forwards and backwards rate of reaction are the same. Therefore, the amounts of substances present in the reacting mixture remain constant.

Question 2

If the forward reaction produces more molecules of gas…

Answer 2

… an increase in pressure decreases the amount of products formed.
…. a decrease in pressure increases the amount of products formed.

Question 3

If the forward reaction produces less molecules of gas…

Answer 3

… an increase in pressure increases the amount of products formed.
… a decrease in pressure decreases the amount of products formed.

Question 4

When does changing the pressure affect a reaction’s equilibrium?

Answer 4

If there are different numbers of molecules of gases on either side of the equation.

Question 5

If the forward reaction is exothermic…

Answer 5

… an increase in temperature decreases the amounts of product formed.
… a decrease in temperature increases the amount of products formed.

Question 6

If the forward reaction is endothermic….

Answer 6

… an increase in temperature increases the amount of products formed.
… a decrease in temperature decreases the amount of products formed.

Question 7

Materials needed to produce ammonia

Answer 7

> Nitrogen from the air

> Hydrogen mainly from natural gas.

Question 8

Conditions needed for the Haber process.

Answer 8

> High temp (about 450 degrees)
High pressure (about 200 atmospheres)
An iron catalyst.

Question 9

Haber process in 5 steps.

Answer 9

1. Gaseous nitrogen + hydrogen enter the machine.
2. The gases are compresses to 200 atom and heated to 450 degrees.
3. Passed over iron catalyst.
4. Emerging mixture is cooled and the ammonia liquefies, separating it from he unseated nitrogen/hydrogen.
5. Unreacted gases return to the beginning.

Question 10

Use of ammonia

Answer 10

Fertilisers

Question 11

Why is a pressure of 200 atmospheres used in the Haber process?

Answer 11

The forward reaction produces less molecules of gas, so to get the maximum yield of ammonia, the pressure has to be as high as possible. However, above 200 atmo, special reaction vessels and pipes have to be used so that there is no danger of explosion. Therefore, to keep the process economical, a compromise is made.

Question 12

Why is a temperature of 450 degrees used for the Haber process?

Answer 12

Because the forward reaction is exothermic, using a low temperature would increase the yield. However, doing so would make the process very slow and not commercially viable. Using a low temperature could also reduce the effectiveness of the iron catalyst.

Question 13

How does the use of a catalyst affect the Haber process?

Answer 13

It speeds up both the forwards and backwards reaction, but has no effect on the actual yield.