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Flashcards in The Haber Process Deck (22):
1

What are the raw materials used in the Haber process?

nitrogen - obtained from the air (which is 78% nitrogen) by fractional distillation, or by burning methane to remove the oxygen

hydrogen - obtained from methane reacting with steam to form carbon dioxide and hydrogen using a nickel catalyst

2

How can nitrogen be obtained?

from the air (which is 78% nitrogen) - liquified air goes through fractional distillation

by burning methane to remove the oxygen

3

How can hydrogen be obtained?

from methane reacting with steam to form carbon monoxide and hydrogen using a nickel catalyst

cracking hydrocarbons

4

What type of reaction is the Haber Process?

a reversible reaction

5

What is the product of the Haber Process?

ammonia (NH3)

6

What is the equation for the Haber Process?

nitrogen + hydrogen ⇌ ammonia

N2 (g) + 3H2 (g) ⇌ 2NH3 (g)

7

What happens to the unreacted nitrogen and hydrogen in the reaction?

they are recylced through the reactor so nothing is wasted

8

What happens the ammonia in the reaction?

the reaction mixture is cooled and the ammonia condenses as a liquid and is removed

9

What is the approximate percentage yield of the Haber Process?

abouyt 15%

10

What are the conditions of the Haber Process?

temperature: 450oC

pressure: 200 atmospheres

catalyst: iron

11

What are the reasons for the proportions of nitrogen and hydrogen?

an excess of either nitrogen or hydrogen would clutter the reaction vessel with molecules which wouldn't have anything to react with

12

Explain the conditions: temperature

N2 (g) + 3H2​ (g) ⇌ 2NH3 (g)

The exothermic reaction (foward reaction) is favoured by a low temperature because the, if you lower the temperature,  the p.o.e. will move to counteract this (move to the right) to produce more heat (Le Chatelier's Principle)

However:

If the temperature is too low, the rate of reaction becomes too slow; it is not economical

A compromise is chosen:

450°C is a compromise temperature producing a reasonably high proportion of ammonia reasonably quickly

13

Explain the conditions: pressure

N2 (g) + 3H2​ (g) ⇌ 2NH3 (g)

There are 4 moles of reactants to 2 moles of product

An increased pressure favours the foward reaction because, if you increase the pressure, the p.o.e. will move to counteract this (move to the right) to lower the pressure (Le Chatelier's Principle)

High pressure also speeds up the reactions as a higher pressure pushes the same amount of gas particles into a smaller volume ensuring that there are more frequent, successful collisions in the same amount of time

However:

Generating high pressures and building plants that can withstand them are expensive

A compromise is chosen

200 atmopsheres gives the best percentage yield of ammonia at a reasonable expense

14

Explain the conditions: catalyst

an iron catalsyt speeds up the rate of reaction by lowering the activation energy, but has no effect on the proportion of ammonia in the equilibrium mixture

the catalyst lowers operating temperatures

if the catalyst wasn't used, the reaction would be so slow that virtually no ammonia would be produced

15

How is ammonia extracted?

ammonia is separated as the reaction mixture is pumped to the condenser where it cools

ammonia has a higher boiling point than nitrogen and hydrogen so it condenses first and is collected as a liquid

the gaseous nitrogen and hydrogen are recycled and pumped back into the reaction chamber

16

What are the uses of ammonia?

making fertilisers

making nitric acid

making nylon

17

How is ammonia used to make fertlisers?

reacting ammonia with nitric acid to get ammonium nitrate:

NH3 (g) + HNO3 (aq) → NH4NO3 (s)

18

Why is ammonium nitrate (NH4NO3) an especially good fertiliser?

it has nitrogen from two sources, the ammonia and the nitric acid

plants need nitrogen to make proteins

this is a much more effective fertiliser than organic alternatives so it helps farmers to produe crops from land taht otherwise wouldn;t have been fertile enough

19

What is the main use of ammonia?

to make fertilisers

most of the ammonia used to make nitric acid eventually ends up in fertilisers as well

20

What do plants convert the nitrogen in fertilisers into?

proteins (amino acids)

21

Use the information form the graph, together with your own knowledge of the process, to explain why many industrial ammonia plants operate at 200 atmospheres and 450oC

high pressure increases the yield but is also expensive

low temperature increases the yield but at low temperatures the rate of reaction is slow

a compromise is chosen: optimum conditions to balance percentage yield of ammonia and rate of reaction

22

State which conditions of temperature and pressure would give the highest percentage yield of ammonia at equilibrium

Explain why

lower temperatures favour the foward reaction because it is exothermic

if the temperature is increased, the yield of product would decrease

higher pressures favour the foward reaction because their are four reactant moles but only two product moles