10– ammonia

Question 1

Decomposition equation to form ammonia

Answer 1

NH4Cl (s) —> NH3 (g) + HCl (g)
HCl (g) + NH3 (g) —> NH4Cl

Question 2

Haber process equation

Answer 2

N2 (g) + 3H2(g) —> 2NH3 (g)
2NH3 (g) —> 3H2(g) + N2 (g)

Question 3

Where to get raw materials required for the Haber process?

Answer 3

Nitrogen: fractional distillation of liquified air
Hydrogen: cracking of crude oil fractions

Question 4

Haber process

Answer 4

1. Nitrogen and hydrogen are mixed in the ratio 1:3 by volume
2. The gas mixture is compressed to 200/250atm
3. The compressed gases flow over the iron catalyst and are heated to 450dgC. Only about 15% of the mixture leaving the chamber is ammonia
4. A mixture of ammonia, unreacted nitrogen and unreacted hydrogen is obtained and cooled
5. Ammonia gas condenses into liquid and is pumped into tanks and stored under pressure (boiling point of ammonia higher than nitrogen and hydrogen thus when cooled, only ammonia condenses, N2 H2 remains gases)
6. Unreacted nitrogen and hydrogen are transferred back into the converter to be recycled for further reaction.

Question 5

Optimal pressure

Answer 5

The higher the pressure, the higher the yield of ammonia. Increase in pressure also increases the rate of reaction. However, maintaining a high pressure incurs a large cost as it requires expensive equipment and a large amount of electricity thus a compromise pressure of 200/250atm is used.

Question 6

Optimal temperature

Answer 6

The lower the temperature, the higher the yield of ammonia. A lower tempt deceases the decomposition of ammonia. However, a lower tempt will decrease the rate of reaction. Thus, a compromise tempt of 450dgC is used.

Question 7

Optimal conditions to manufacture ammonia thru Haber process

Answer 7

200/250atm
450dgC
Finely divided iron catalyst

Question 8

Alternate ways to obtain ammonia

Answer 8

Displacement of ammonia from its salts

NH4Cl (aq) + NaOH (aq) -> NaCl (aq) + NH3 (g) + H2O (l)

Question 9

Explain in terms of collision betw particles, how a lower pressure affects the rate of reaction in the reactor

Answer 9

A lower pressure will decrease the number of reacting particles per unit volume, hence decreasing the frequency of effective collisions between reacting particles. Thus, the rate of reaction will decrease.

Question 10

Use the graph (%yield of ammonia—pressure graph) to predict how a lower pressure affects the relative amounts of ammonia, nitrogen and hydrogen that leave the main reactor. Explain your reasoning.

Answer 10

Using info from the graph, at 550dgC, when pressure decreases from 200atm to 100atm, the yield of ammonia decreases from approximately 15% to 7.5%, hence a lower pressure will decrease the yield of ammonia. Therefore, the relative amount of ammonia decreases. Thus, relative amount of nitrogen and hydrogen that leaves the main reactor.

Question 11

What effect does a lower pressure have on the final amount of ammonia made from a fixed amount of nitrogen and hydrogen? Explain your reasoning.

Answer 11

A lower pressure will have no effect on the final amount of ammonia made. The final amount of ammonia obtained is dependent on the amount of nitrogen and hydrogen and not the pressure. As the nitrogen and hydrogen are recycled into the reactor and their total amount is fixed, the final amount of ammonia obtained will be fixed.