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EdExcel GCSE Chemistry > Dynamic Equilibria - Topic 5 > Flashcards

Dynamic Equilibria - Topic 5 Flashcards

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1
Q

Haber process:

A
  • a reversible reaction between nitrogen and hydrogen to form ammonia
  • the reaction is reversible so ammonia breaks down again into nitrogen and hydrogen
  • nitrogen + hydrogen ⇌ ammonia
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2
Q

Enthalpy change:

A
  • heat energy change at constant pressure
  • △H
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3
Q

How does temperature affect the rate of attainment of equilibrium?

A
  • a higher temperature
  • particles have more kinetic energy → move faster → more frequent collisions → more frequent and successful collisions in given time → more reactions in given time
  • equilibrium reached at a faster rate
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4
Q

How does pressure/concentration affect the rate of attainment of equilibrium?

A
  • higher pressure/concentration → gas molecules closer together/more concentrated → more frequent collisions → more frequent successful collisions
  • equilibrium reached at faster rate
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5
Q

How do catalysts affect the rate of attainment of equilibrium?

A
  • catalysts speed up chemical reactions without being used up
  • they work by providing an alternative E pathway with a lower activation E
  • higher proportion of collisions successful → more successful collision in given time → more reactions in given time → therefore, catalyst speeds up rate at which eqm is reached
  • they do not affect the position of eqm as they speed up both the forward and reverse reactions by the same amount so does not affect yield
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6
Q

Conditions required for the Haber process:

A
  • iron catalyst - which purified gases are passed over
  • temperature 450 degrees C
  • pressure 200 atmospheres (ATM)
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7
Q

How are the conditions of industrial reactions e.g. the Haber process related to the availability and cost of raw materials and energy supplies?

A
  • catalyst is used because of the effect of having an increased rate of reaction - but also expensive
  • high temperatures and pressures can be expensive and dangerous as well (particularly pressure - explosions) and the equipment required for them can be very expensive
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8
Q

How does the control of temperature and pressure produce an acceptable yield in an acceptable time for the Haber process?

A
  • high temperatures and pressures are desired for industrial reactions to increase the rate of reaction and the rate at which the equilibrium is attained
  • but a higher temperature shifts equilibrium towards the reactants (as the forwards reaction is exothermic) - lower yield
  • therefore a compromise is required to ensure a fast rate of reaction and high yield of products - high temp → low yield → maximised product/time
  • high pressure - > increased rate → reasonable cost + risk
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9
Q

What are the conditions that give highest percentage of ammonia and why is it a problem?

A
  • low temperature + high pressure
  • low temperature - rate of react v. slow
  • high pressure - dangerous + expensive
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10
Q

How does an iron catalyst produce an acceptable yield in an acceptable time for the Haber process?

A
  • does not change position of equilibrium
  • increases the rate of attainment of equilibrium
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11
Q

Reasons that a low yield is not a problem in the Haber process:

A
  • unreactive gas is recycled
  • rate is high
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12
Q

What may fertilisers contain and why?

A

fertilisers may contain nitrogen, phosphorous and potassium compounds to promote plant growth

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13
Q

NPK fertilisers:

A

nitrogen, phosphorous and potassium fertilisers

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14
Q

Why is phosphorous used in fertilisers?

A

DNA, growth, roots

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15
Q

Why is potassium used in fertilisers?

A

promotes fruiting + flowering

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16
Q

Why is nitrogen used in fertilisers?

A
  • used in biological molecules e.g. proteins and DNA in living creatures
  • very few living creatures able to make use of huge amount of nitrogen in atmosphere
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17
Q

Problems with nitrogen compounds:

A
  • eutrophication
  • fertilisers washed into rivers + lakes
  • algae grows
  • kills plants + marine life
18
Q

Why are ammonium nitrate compounds used as fertilisers?

A
  • most plants require soluble nitrogen compounds to supply their nitrogen intake
  • natural sources of nitrogen compounds include manure and compost - however, these natural sources of fertiliser are not sufficient to grow enough food for the world’s growing population
  • ammonia is a soluble nitrogen compound but is not suitable to be used as a nitrogen fertiliser as it is alkaline and escapes easily from the soil as it is a gas
  • ammonia can be turned into a suitable fertiliser by reacting it with an acid
19
Q

Why is nitrogen a gas at room temperature?

A

weak intermolecular forces → require little E to over → low m.p. and b.p.

20
Q

Why is nitrogen so unreactive?

A

has strong tripple covalent bond between atoms → large amount of E required to overcome the bonds

21
Q

Why are harmful NOx gases produced in car engines if nitrogen is unreactive?

A

car engines involve v. high temps and pressure so N2 will react with O2

22
Q

How does ammonia react with nitric acid to produce a salt that is used as a fertiliser?

A
  • ammonia can be used to manufacture salts with nitric acid
  • ammonia acts as a base
  • ammonia + nitric acid —> ammonium nitrate
  • NH3 + HNO3 → NH4NO3
23
Q

How is the reaction of ammonia and an acid different from other neutralisation reactions?

A
  • normally acid + base ——> salt + water
  • no water produced
24
Q

Why are the ammonium salts better fertilisers than ammonia?

A
  • neutral - not alkaline
  • less toxic
  • don’t escape/evaporates quickly
25
Q

Method for laboratory preparation of ammonium sulphate:

A
  • Use glass pipette to put 25cm3 of ammonia solution into conical flask
  • Add methyl orange - turns yellow
  • Fill burette with H2SO4 and add to conical flask
  • Near endpoint add drop-wise and swirl flask
  • Indicator turns orange
  • Repeat using same volumes but without indicator
  • Heat/Leave water to evaporate leaving solid NH4NO3
  • (only few stages - titration and then crystallisation)
26
Q

Reactants for the laboratory preparation of ammonium sulphate:

A
  • ammonia solution + dilute sulphuric acid
  • bought from chemical manufacturers
27
Q

What is the scale of the laboratory preparation of ammonium sulphate?

A
  • small scale - very little is produced
  • ammonia and sulphuric acid solutions were below concentration (0.1M) for safety reasons
  • milligrams
28
Q

What is the equipment used for the laboratory preparation of ammonium sulphate?

A

burette, pipette, flasks etc. were made out of glass

29
Q

How fast is the laboratory preparation of ammonium sulphate?

A
  • titration was carried out slowly and carefully until indicator just changed colour from yellow to orange
  • ammonium sulphate solution was left for a several days to crystallised, producing a batch
30
Q

What are the conditions required for the laboratory preparation of ammonium sulphate?

A
  • room temperature + pressure
  • dilute solutions
31
Q

What type of reaction was the laboratory preparation of ammonium sulphate?

A

batch

32
Q

How is ammonium sulphate produced industrially?

A
  • the ammonia and sulphuric acid are imported on a very large scale (tonnes)
  • The reactants are continually piped into larger reaction towers, where concentrated sulphuric acid is sprayed onto anhydrous ammonia gas at 60 degrees C
  • The pipes and reaction vessels are made of thick stainless steel to withstand high pressures and highly corrosive nature of reactants
  • The factory is designed to minimised risk of explosion from highly exothermic process
  • A slurry of ammonium sulphate is blown through hot air to produce small pellets of the fertiliser
  • Care is taken to adjust the size of the pellets so they do not jam or break farming machinery
  • (many stages required - need to make and ammonia and sulphuric acids, react accurate volumes then evaporate)
33
Q

Reactants for the industrial preparation of ammonium sulphate:

A

natural gas, air, water (to make ammonia) and sulphur, air, water (to make sulphuric acid)

34
Q

What is the scale of the industrial preparation of ammonium sulphate?

A
  • large scale - produces a lot
  • tonnes
35
Q

What are the hazards of the industrial preparation of ammonium sulphate?

A
  • dangerous - high pressure, explosive
  • corrosive
36
Q

What is the equipment used for the industrial preparation of ammonium sulphate?

A

thick stainless steel

37
Q

What are the conditions required for the industrial preparation of ammonium sulphate?

A
  • 60 degrees C
  • high pressure
38
Q

What type of process is the industrial preparation of ammonium sulphate?

A

continuous

39
Q

Similarities between industrial and laboratory preparation of ammonium sulphate:

A
  • both use sulphuric acid
  • both neutralisation
40
Q

Différences between industrial and laboratory preparation of ammonium sulphate:

A
  • industrial process on much larger scale than laboratory process
  • industrial process involves more stages than laboratory process
  • ammonia is a gas in the industrial process but a solution in the laboratory process
  • laboratory preparation uses titration and crystallisation unlike industrial process
41
Q

Dynamic equilibria:

A

Both forward and backward reactions taking place at same time

EdExcel GCSE Chemistry (29 decks)

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