C7.4 Introducing dynamic equilibrium Flashcards
1
Q
- What is the symbol for reversible reactions?
A
↔
2
Q
- What is a reversible reaction?
A
-a reaction where the products can react to produce the reactants
3
Q
- What happens if a reversible reaction takes place in a closed system?
A
-the reversible reaction can reach a state of equilibrium
4
Q
- In what conditions can a reversible reaction reach a state of equilibrium?
A
-in a closed system
none of the reactants or products can escape
5
Q
- What does the term ‘closed system’ mean?
A
-none of the reactants or products can escape
6
Q
- What does equilibrium mean?
A
-the relative (%) quantities of reactants and products will reach a certain balance and stay there
7
Q
- What is a dynamic equilibrium?
A
- reactions are still taking place in both directions AT THE SAME RATE
- reactions both ways cancel each other out= no overall effect
8
Q
- What are the feedstocks for the Haber process?
A
- nitrogen
- hydrogen
9
Q
- How are the feedstocks for the Haber process obtained?
A
- nitrogen: the air (78% nitrogen)
- hydrogen: cracking of chemicals in natural gas using steam
10
Q
- What are the industrial conditions for the Haber process?
A
- pressure= 200 atmospheres
- temperature= 450⁰
- catalyst= iron
11
Q
- What is the symbol equation for the Haber process?
A
N2 + 3H2 ↔ 2NH3 (+heat)
12
Q
- What is the word equation for the Haber process?
A
-nitrogen + hydrogen ↔ ammonia (+heat)
13
Q
- What is the reaction between hydrogen and nitrogen to form ammonia in the Haber process?
A
-a reversible reaction
14
Q
- What does the Haber process being reversible cause?
A
-not all nitrogen and hydrogen will convert into ammonia
15
Q
- How is the yield of ammonia increased in the Haber process?
A
- by recycling unreacted hydrogen and nitrogen, so nothing is wasted
- (more product produced using the same amount of reactant)
16
Q
- What is the effect of changing pressure on the yield of ammonia at equilibrium in the Haber process?
A
-high pressures favour the forward reaction (because four molecules of gas on left and 2 on right)= increase yield
17
Q
- What is the effect of changing temperature on the yield of ammonia at equilibrium in the Haber process?
A
- lower temperatures= increase yield
- as forward reaction is exothermic so increasing temp would move equilibrium the wrong way
18
Q
- Do gases in the Haber process reach equilibrium?
A
-gases do not stay in the reactor long enough to reach equilibrium
19
Q
- What is used to increase the rate of reaction in the Haber process?
A
-an iron catalyst
=increase rate of reaction= ammonia produced faster
20
Q
- How are conditions in the Haber process a compromise to produce an economically viable yield of ammonia?
A
- pressure: high as possible to increase % yield/ without being too expensive to build= 200 atmospheres
- temperature: compromise between maximum yield and rate of reaction- decrease temp to increase rate of reaction/ increase temp to increase speed of reaction= 450⁰
21
Q
- What living organisms ‘fix’ nitrogen at room temperature and pressure using enzymes as catalysts?
A
-Nitrogen-fixing bacteria
22
Q
- How does a nitrogen-fixing bacterium ‘fix’ nitrogen?
A
-‘fix’ nitrogen at room temperature and pressure using enzymes as biological catalysts
23
Q
- What is an example of a biological catalyst?
A
-enzymes
24
Q
- Under what conditions is the Haber process done?
A
-high temperatures and pressures turn nitrogen and hydrogen into ammonia
25
8. What catalyst is used in the Haber process and why?
- iron catalyst speeds up making ammonia
| - without it the temperature would have to be raised= decrease percentage yield
26
8. Why are chemists interested in producing new catalysts that mimic natural enzymes?
-so processes like the Haber process could be at room temperature and pressure
= cheaper and more efficient
27
9. What are the uses of nitrogen fixation (e.g. from the Haber process)?
- ammonia used for fertilisers = increase crop yield= increase world food production
- ammonia used in industry (make plastics, explosives, pharmaceuticals)
28
9. What is the negative impact on the environment of the large scale manufacture of ammonia and the widespread use of fertilisers made from it?
-large amount so fertilisers pollute water supplies and cause eutrophication (algae growth causing death of plants and animals)
29
9. What is eutrophication?
```
-fertilisers leach into lakes and rivers
=rapid algae growth
=blocks out light to other plants
=microorganisms feed on dead plans using oxygen
=fish die from lack of oxygen
=everything dies
```
30
10. How sustainable is the nitrogen fixation processes?
1- whether or not the feedstock is renewable: hydrogen non-renewable as from fossil fuels, nitrogen renewable as from air
2- the atom economy: all H2 and N2 makes ammonia= amazing atom economy
3- the nature and amount of by-products or wastes and what happens to them: no waste as chemicals all recycled
4- the energy inputs or outputs: lots of energy needed for high temperatures (450⁰)
5- the environmental impact: fertilisers from NH3 (ammonia)= water pollution
6- the health and safety risks: high pressure/temperatures= dangerous
7- the social and economic benefits: very profitable
31
4. Why is fixing nitrogen by the Haber process important?
-the nitrogen in plants would normally be returned to the soil when it had died, however we harvest the crops so the nitrogen is not returned to soil= we need fertilisers with nitrogen for plants to grow so we don’t starve
32
6. What can the efficiency of the Haber process be improved by?
-by using a different catalyst (to mimic natural enzymes)
=be produced at room temperature and pressure
=cheaper and more efficient
