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FINISHED > C7.4 Introducing dynamic equilibrium > Flashcards

C7.4 Introducing dynamic equilibrium Flashcards

1
Q
  1. What is the symbol for reversible reactions?
A

↔

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2
Q
  1. What is a reversible reaction?
A

-a reaction where the products can react to produce the reactants

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3
Q
  1. What happens if a reversible reaction takes place in a closed system?
A

-the reversible reaction can reach a state of equilibrium

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4
Q
  1. 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

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5
Q
  1. What does the term ‘closed system’ mean?
A

-none of the reactants or products can escape

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6
Q
  1. What does equilibrium mean?
A

-the relative (%) quantities of reactants and products will reach a certain balance and stay there

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7
Q
  1. 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
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8
Q
  1. What are the feedstocks for the Haber process?
A
  • nitrogen

- hydrogen

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9
Q
  1. How are the feedstocks for the Haber process obtained?
A
  • nitrogen: the air (78% nitrogen)

- hydrogen: cracking of chemicals in natural gas using steam

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10
Q
  1. What are the industrial conditions for the Haber process?
A
  • pressure= 200 atmospheres
  • temperature= 450⁰
  • catalyst= iron
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11
Q
  1. What is the symbol equation for the Haber process?
A

N2 + 3H2 ↔ 2NH3 (+heat)

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12
Q
  1. What is the word equation for the Haber process?
A

-nitrogen + hydrogen ↔ ammonia (+heat)

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13
Q
  1. What is the reaction between hydrogen and nitrogen to form ammonia in the Haber process?
A

-a reversible reaction

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14
Q
  1. What does the Haber process being reversible cause?
A

-not all nitrogen and hydrogen will convert into ammonia

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15
Q
  1. 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)
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16
Q
  1. 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
  1. 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
  1. Do gases in the Haber process reach equilibrium?
A

-gases do not stay in the reactor long enough to reach equilibrium

19
Q
  1. 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
  1. 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
  1. What living organisms ‘fix’ nitrogen at room temperature and pressure using enzymes as catalysts?
A

-Nitrogen-fixing bacteria

22
Q
  1. How does a nitrogen-fixing bacterium ‘fix’ nitrogen?
A

-‘fix’ nitrogen at room temperature and pressure using enzymes as biological catalysts

23
Q
  1. What is an example of a biological catalyst?
A

-enzymes

24
Q
  1. Under what conditions is the Haber process done?
A

-high temperatures and pressures turn nitrogen and hydrogen into ammonia

25
Q
  1. What catalyst is used in the Haber process and why?
A
  • iron catalyst speeds up making ammonia

- without it the temperature would have to be raised= decrease percentage yield

26
Q
  1. Why are chemists interested in producing new catalysts that mimic natural enzymes?
A

-so processes like the Haber process could be at room temperature and pressure
= cheaper and more efficient

27
Q
  1. What are the uses of nitrogen fixation (e.g. from the Haber process)?
A
  • ammonia used for fertilisers = increase crop yield= increase world food production
  • ammonia used in industry (make plastics, explosives, pharmaceuticals)
28
Q
  1. What is the negative impact on the environment of the large scale manufacture of ammonia and the widespread use of fertilisers made from it?
A

-large amount so fertilisers pollute water supplies and cause eutrophication (algae growth causing death of plants and animals)

29
Q
  1. What is eutrophication?
A 
-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
Q
  1. How sustainable is the nitrogen fixation processes?
A

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
Q
  1. Why is fixing nitrogen by the Haber process important?
A

-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
Q
  1. What can the efficiency of the Haber process be improved by?
A

-by using a different catalyst (to mimic natural enzymes)
=be produced at room temperature and pressure
=cheaper and more efficient

FINISHED (11 decks)

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