Topic 4 - Equilibria, Obtaining/using Metals & Reversible Reactions

Question 1

Most metals are extracted from ores found in the Earth’s crust.
The method used to extract a metal from its ore is linked to the reactivity of the metal.
Aluminium is extracted from its ore by electrolysis.
Iron is extracted from its ore by heating with carbon.
Both metals can also be obtained by recycling.
Explain the advantages of recycling aluminium and iron rather than extracting them from
their ores. (6)

Answer 1

• recycling conserves raw materials/natural resources
• less power/energy used
• therefore conserves fossil fuels
• reduces waste in landfill sites
• mining for ores avoided
• less damage to habitats/landscape
• less energy required to melt and reform metals than to extract them
• produces less carbon dioxide than extracting/ reduces carbon footprint
• carbon dioxide is a greenhouse gas
• greenhouse gases cause global warming
• avoids use of large amounts of electricity to extract aluminium from its ore
• electricity is expensive
• avoids release of carbon dioxide when carbon burns
• avoids use of large amounts of heat energy needed to extract iron from its ore

Question 2

metal + sulfuric acid → metal sulfate + hydrogen
When metal Y reacts with dilute sulfuric acid, bubbles form quickly at first and then the
reaction stops.
Most of the solid metal remains.
Explain why the reaction between metal Y and excess dilute sulfuric acid stopped even
though there was solid metal Y left. (2)

Answer 2

Metal insoluble/coats the metal/forms a barrier (1)
Prevents further reaction of metal with acid (1)

Question 3

The reactivity of copper, magnesium and zinc was investigated.
Each metal was placed separately in dilute hydrochloric acid.
The amount of effervescence was observed. State 2 variables, apart from the mass of the metals, that should be controlled in this
investigation. (2)

Answer 3

Same volume of acid (1)
Same concentration of acid (1)
Same size of metal pieces (1)
Same temperature (1)

Question 4

magnesium reacts with dilute hydrochloric acid to form magnesium chloride solution
and hydrogen gas.
The equation for the reaction is
Mg(s) + 2HCl(aq) → MgCl2(………) + H2(……..)
Fill in the missing state symbols in the spaces provided. (2)

Answer 4

Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)

Question 5

Some metals are found in the Earth’s crust as uncombined elements.
Reactive metals are found in ores.
In ores, metals are combined with other elements.
An ore of iron is mostly iron oxide, Fe2O3.
Iron can be extracted from this iron oxide by heating it with carbon.
Balance this equation: (2)
2Fe2O3 + ….C → ….Fe + ….CO2

Answer 5

2Fe2O3 + 3C → 4Fe + 3CO2
(2)

Question 6

Nickel is extracted from nickel compounds.
State an advantage of extracting nickel by phytoextraction rather than from its ore. (1)

Answer 6

Decontaminates ground/conserves nickel ores (1)
Less noise due to mining/carbon neutral (1)

Question 7

The order of reactivity of copper, magnesium and zinc can be determined by the displacement reactions between these metals and solutions of their salts.
You are provided with:
• samples of the three metals
• solutions of copper sulfate, magnesium sulfate and zinc sulfate.
Describe the experiments that can be done to determine the order of reactivity of these
metals by displacement reactions. (3)

Answer 7

Place separate pieces of each metal into solutions of each solution (1)
Observe changes in appearance/colour of metal/solution (1)
The more reactive metal shows the most reactions (1)

Question 8

The method used to extract a metal from its ore depends on the position of the metal in the
reactivity series.
Copper is low down in the reactivity series and can be obtained from copper oxide.
Devise a simple method to obtain a sample of copper from copper oxide in the laboratory. (2)

Answer 8

mix copper oxide with carbon/powdered charcoal (1)
heat with carbon (strongly until no further change) (1)
+
react copper oxide with dilute sulfuric/hydrochloric acid (1)
electrolyse the solution formed (1)
OR
pass hydrogen/methane) (1)
over heated copper oxide (1)

Question 9

The method used to extract a metal from its ore depends on the position of the metal in the
reactivity series.
One step in the extraction of titanium metal involves the displacement reaction between
titanium chloride, TiCl4, and magnesium.
TiCl4 + 2Mg → Ti + 2MgCl2
This equation can be simplified as
Ti4+ + 2Mg → Ti + 2Mg2+
Explain why this displacement reaction can be described as a redox reaction. (3)

Answer 9

Redox involves both reduction and oxidation (1)
Magnesium atoms loses electrons (1)
Titanium ions accept electrons (1)

Question 10

The formula of the sulfate ion is SO42−
Which of the following is the formula of titanium sulfate containing the Ti4+ ion? (1)

A TiSO4
B Ti2SO4
C Ti(SO4)2
D Ti2S2O8

Answer 10

Ti(SO4)2

Question 11

Some metals are found in the Earth’s crust as uncombined elements.
Reactive metals are found in ores.
(metals are combined with other elements.)
In one stage of the extraction of lead from its ore, lead oxide is heated strongly with carbon.
2PbO + C → 2Pb + CO2
Explain, using this equation, which substance has been oxidised in this reaction. (2(

Answer 11

Carbon (1)
Gained oxygen to form carbon dioxide (1)

Question 12

Metals can be extracted from ores found in the Earth’s crust.
Explain why aluminium cannot be extracted from its ore by heating with carbon but can be
extracted by electrolysis. (2)

Answer 12

Aluminium is more reactive than carbon (1)
Carbon can’t remove the oxygen/no reaction between carbon and aluminium oxide/carbon can’t displace aluminium (1)
Electrolysis can be used to reduce aluminium ions (1)

Question 13

The method used to extract a metal from its ore depends on the position of the metal in the
reactivity series.
Aluminium is extracted from its ore by electrolysis.
Explain why this method is used to extract aluminium from its ore. (2)

Answer 13

Aluminium is very high in the reactivity series/very reactive (1)
Needs a lot of energy (to remove oxygen from oxide) (1)

Question 14

Iron ore contains iron oxide.
Iron is extracted from iron oxide by heating the oxide with carbon.
In this reaction (1)
A carbon is reduced
B iron oxide is neutralised
C iron oxide is reduced
D iron is oxidised

Iron oxide + carbon → iron + carbon dioxide

Answer 14

iron oxide is reduced

Question 15

The method used to extract a metal from its ore depends on the position of the metal in the
reactivity series.
Phytoextraction is an alternative biological method that can be used to extract metals from very low-grade ores.
Give one disadvantage of phytoextraction as a method of extraction of metals. (1)

Answer 15

Slow process (1)
Large area of land required (1)
Only extracts metal from the ground surface (1)
Metal needs further extraction (1)

Question 16

The formula of aluminium oxide is Al2O3.
Give the number of ions in the formula Al2O3. (1)

Answer 16

5

Question 17

Complete the balanced equation (2)

2Al2O3 → ……………. Al + ……………. O2

Answer 17

2Al2O3 → 4Al + 3O2

Question 18

Some metals are found in the Earth’s crust as uncombined elements.
Reactive metals are found in ores.
In ores, metals are combined with other elements.
Give two advantages of recycling metals rather than extracting metals from their ores. (2)

Answer 18

Preserves ore reserves (1)
Reduces waste (1)
Reduces energy needed for metal extraction (1)
Preserves habitats/landscapes/resources (1)

Question 19

Metals are extracted from substances naturally occurring in the Earth’s crust.
The environmental impact of a product is assessed in a life-cycle assessment.
The stages are not in the correct order:
A disposal of the product
B manufacturing the product
C obtaining and processing the raw materials
D using the product
List the stages of the life-cycle assessment in the correct order (2)

Answer 19

CBDA

Question 20

Most metals are extracted from ores found in the Earth’s crust.
The method used to extract a metal from its ore is linked to the reactivity of the metal.
Part of the reactivity series is shown below:
Predict the method that will have to be used to extract calcium from its ore. (1)

Calcium - aluminium - zinc - iron - copper - gold

Answer 20

Electrolysis

Question 21

In recent years, researchers have been investigating alternative methods of extracting
metals from soils.
Researchers have found that growing certain plants in appropriate areas can result in the
phytoextraction of copper.
Describe how growing plants can result in the phytoextraction of copper. (2)

Answer 21

Plants absorb copper/metal ions from the soil/ores/plants concentrate copper ions (1)
Plants are burned to leave metal compound (1)

Question 22

Calcium and potassium react with water in similar ways.
One similarity in the reactions is that hydrogen gas is produced.
State one other similarity in the products of the reactions of calcium and potassium with water. (1)

Answer 22

Both form a hydroxide

Question 23

Potassium is higher in the reactivity series than calcium and reacts more vigorously with water than calcium reacts with water.
State why potassium is higher in the reactivity series and reacts more vigorously with water than calcium. (1)

Answer 23

Potassium forms cations/loses outer electrons more easily

Question 24

Iron is extracted by heating iron oxide with carbon.
Electrolysis of molten iron oxide is not used to extract iron.
State why iron can be extracted by heating iron oxide with carbon. (1)

Answer 24

Iron is reactive than carbon (1)

Question 25

State why electrolysis is not used to extract iron. (1)

Answer 25

Electrolysis is expensive/a more expensive method than heating with carbon/electrolyse requires a large amount of electricity

Question 26

In the first stage of extracting nickel from nickel sulfide, the nickel sulfide, NiS, is heated in air to form nickel oxide, NiO, and sulfur dioxide.
Write the balanced equation for this reaction (2)

Answer 26

2NiS + 3O2 → 2NiO + 2SO2

Question 27

In the final stage of the extraction process, a nickel compound is electrolysed to produce
pure nickel.
An advantage of producing a metal by electrolysis is that (1)

A electrolysis uses a large amount of electricity
B the metal produced by electrolysis is very pure
C electrolysis is a very cheap method of extraction
D electrolysis is the only method of extracting unreactive metals

Answer 27

the metal produced by electrolysis is very pure

Question 28

Metals are extracted from substances naturally occurring in the Earth’s crust.
Zinc can be extracted by heating zinc oxide with carbon.
The products are zinc and carbon dioxide.
Write the word equation for this reaction. (2;

Answer 28

Zinc oxide + carbon → zinc + carbon dioxide

Question 29

When chloride ions are added to a pale blue solution containing copper ions, the mixture
turns yellow.
pale blue solution + chloride ions ↔ yellow solution + water
What effect does the removal of chloride ions have on the colour of the yellow mixture? (1)
A does not change colour
B turns blue
C turns colourless
D turns darker yellow

Answer 29

turns blue

Question 30

The industrial production of sulfuric acid involves several steps.
One of these steps is the reaction of sulfur dioxide, SO2, with oxygen to form sulfur trioxide, SO3.
2SO2(g) + O2(g) ↔️ 2SO3(g)
The reaction to produce sulfur trioxide reaches an equilibrium.
The forward reaction is exothermic.
The rate of attainment of equilibrium and the equilibrium yield of sulfur trioxide
are affected by pressure and temperature.
A manufacturer considered two sets of conditions, A and B, for this reaction.
In each case sulfur dioxide is mixed with excess oxygen.
The manufacturer changed the temperature and the pressure and only used a catalyst in B.
The sets of conditions A and B are shown below:
A - 2 atm, 680’ temperature, no catalyst used
B - 4 atm, 425’ temperature, catalyst used
The manufacturer chooses set of conditions B rather than set of conditions A.
Explain, by considering the effect of changing the conditions on the rate of attainment of
equilibrium and on the equilibrium yield of sulfur trioxide, why the manufacturer chooses the set of conditions B rather than A. (6)

Answer 30

• equilibrium reached faster because of higher temperature in set A / equilibrium reached slower because of lower temperature in set B
• higher temperature means more frequent collisions because molecules have more energy / ORA for lower temperature in set B
• decrease in temperature increases equilibrium yield but system takes longer to reach equilibrium
• temperature chosen for optimum conditions
• yield lower as forward reaction is exothermic
• high temperature favours back reaction which is endothermic
• equilibrium reached faster because of higher pressure in set B / equilibrium reached slower because of lower pressure in set A
• higher pressure causes molecules to be closer together so more frequent collisions / ORA for lower pressure in set A
• yield higher because products occupy smaller volume than reactants for set B
• catalyst in set B causes equilibrium to be reached faster
• catalyst increases rate of both forward and back reactions
• equilibrium position not affected so catalyst does not affect yield
• catalyst reduces the need for the Nailer temperature

Question 31

Hydrated copper sulfate, CuSO4.5H2O, is a blue solid.
Anhydrous copper sulfate, CuSO4, is a white solid.
Heat energy is needed to convert hydrated copper sulfate to anhydrous copper sulfate.
This is a reversible reaction.
Devise an experiment to show that this is a reversible reaction. (4)

Answer 31

Decomposition:
Heat the hydrated crystals (1)
Solid goes white/steam is observed/water produced (1)
Reverse reaction:
Add water/water reacts with anhydrous solid (1)
Solid goes blue again/heat is released (1)

Question 32

Hydrogen reacts with iodine to form hydrogen iodide.
Iodine gas is purple and hydrogen iodide gas is colourless. Hydrogen and iodine are placed in a sealed container. The container is left until equilibrium is reached.
The conditions are changed favouring the forward reaction.
Explain what you would see. (2)

Answer 32

Less purple/lighter/paler/fades (1)
Because less iodide (1)

Question 33

Ammonia is manufactured by the Haber process. The equation for the reaction is
N2(g) + 3H2(g) ↔ 2NH3(g)
The reaction is reversible and can reach equilibrium.
An iron catalyst can be used in the reaction.
What happens to the rate of attainment of equilibrium and the equilibrium yield of ammonia by adding the iron catalyst? (2)

Answer 33

Rate of attainment of equilibrium increases (1)
Equilibrium yield of ammonia doesn’t change (1)

Question 34

The Haber process reaction is carried out at a pressure of 200 atmospheres.
Explain what effect a pressure higher than 200 atmospheres would have on the rate of attainment of equilibrium and on the equilibrium yield of ammonia. (4)

Answer 34

Rate of attainment of equilibrium increases (1)
Equilibrium yield increases (1)
Equilibrium shifts to the right/products (2)
Decrease the number of molecules (1)

Question 35

The reaction between nitrogen and hydrogen is exothermic.
If nitrogen and hydrogen were reacted at 150 atm pressure and 300 °C, without a catalyst, some ammonia would be formed.
In the Haber process a pressure of 150 atm and a temperature of 450 °C are used, in the presence of an iron catalyst.
Explain why the conditions used in the Haber process are better than the first set of conditions for the manufacture of ammonia. (6)

Answer 35

• higher temperature reaches equilibrium faster because molecules move faster
• therefore there are more frequent collisions because molecules have more energy
• therefore more collisions have required energy but yield will be lower
• because higher temperature favours endothermic reaction and so equilibrium shifts to left hand side
• which is decomposition of ammonia / ammonia reforms elements
• catalyst causes reaction to reach equilibrium faster / catalyst increases rates (of both forward and back reactions)
• lowers the activation energy (of both forward and back reactions) but does not affect yield
• equilibrium position not affected.

Question 36

Methane reacts with steam to form hydrogen and carbon dioxide.
The reaction takes place in two stages.
Stage 1 takes in heat energy, it is endothermic.
Explain the effect of increasing the temperature on the yield of the products of stage 1. (2)
Stage 1 = CH4(g) + H2O ↔️ 3H2(g) + CO(g)
Stage 2 = CH(g) + H2O ↔️ H2(g) + CO2(g)

Answer 36

Shift equilibrium to the right/forward direction (1)
Increase yield of product/hydrogen/carbon monoxide (1)

Question 37

Sulfur trioxide is produced by reacting sulfur dioxide with oxygen.
This reaction takes place in industry at 1–2 atm pressure and can reach a dynamic equilibrium.
Explain the effect on the rate of attainment of equilibrium, if the process is carried out at a
pressure higher than 1–2 atm. (3)

Answer 37

Rate increased/time to reach equilibrium reduced (1)
Because gas molecules are closer/more concentrated (1)
So increased collision rate/more frequent collisions (1)

Question 38

Ammonia is reacted with oxygen to form
nitrogen oxide and water.
Heat energy is given out when ammonia reacts with oxygen.
The conditions chosen for the reaction are
• excess air, rather than just the right amount
• a pressure of 10 atm, rather than atmospheric pressure
• a temperature of 900 °C, rather than room temperature.
Explain the effect of the conditions chosen on the equilibrium yield of nitrogen oxide and on
the rate of attainment of equilibrium. (6)

Answer 38

EXCESS AIR
• increases oxygen concentration
• so excess air favours right hand side
• and gives higher yield
• excess air increases concentration of oxygen
• equilibrium reached faster
PRESSURE
• 9 molecules on left and 1.0 on right
• so higher pressure favours left hand side
• and gives lower yield
• higher pressure increases concentration of gases
• more frequent collisions
• equilibrium reached faster
TEMPERATURE
• heat energy given out in forward reaction
• higher temperature favours reaction that takes in heat energy
• so higher temperature favours left hand side
• hence lower yield
• molecules move faster at higher temperature • more frequent collisions
• therefore more reactions in given time
• equilibrium reached faster

Question 39

The hydrogen used in a hydrogen-oxygen fuel cell can be produced from methanol, CH3OH.
CH3OH + H2O ↔ CO2 + 3H2
In this reaction the forward reaction is endothermic and heat energy is taken in from the surroundings. The conditions are:
• a nickel catalyst
• a temperature of 220 °C
Explain, in terms of their effects on the rate of attainment of equilibrium and the equilibrium
yield of hydrogen, why the reaction is carried out using a catalyst at 220 °C rather than without a catalyst at a lower temperature. (6)

Answer 39

(effect of using a catalyst)
• increases rate of attainment of equilibrium
• increasing rate of both forward and back reaction
• lowers activation energy
• provides an alternative reaction pathway
• no effect on equilibrium yield
(effects of using a temperature of 220 C rather than lower temperatures)
• equilibrium attained in a shorter period of time / faster rate of attainment of equilibrium
• because particles move faster/ have higher (kinetic) energy
• increased collision frequency and more energetic collisions
• equilibrium yield of hydrogen increases with higher temperatures
• because heat energy is taken in the forward reaction (endothermic)
• increasing the temperature shifts equilibrium further to the right-hand side

Question 40

Drinks are often sold in cans.
These cans are made either of aluminium or of steel coated with tin.
The table gives information about these three metallic substances.

aluminium - £1.31, 8% in earth’s crust
steel (iron) - £0.32, 5% in earth’s crust
tin - £12.60, 0.0002% in earth’s crust

Use the table to give two reasons why it could be more important to recycle tin than to recycle aluminium or steel. (2)

Answer 40

Tin is more expensive than aluminium/steel (1)
Amount of tin in earth smaller than aluminium/steel (1)

Question 41

The reaction for the extraction of aluminium from its ore involves (1)
A heating with carbon
B thermal decomposition
C reduction
D neutralisation

Answer 41

reduction

Question 42

Explain, in terms of their structures, why magnalium is stronger than pure aluminium. (3)

Answer 42

in pure metal/aluminium atoms are all same size (1)
in pure metal/aluminium {layers/sheets/atoms} {slide/slip/move} over one another easily(1)
magnesium atoms larger (1)
disrupt {layers/structure/arrangeme nt} of aluminium atoms (1)
prevent {layers/sheets/atoms} {slip/slide/move} (1)

Question 43

Aluminium is extracted by the electrolysis of a molten mixture of its ore (bauxite) and cryolite.
Iron is extracted by heating a mixture of its ore and carbon.
Explain why electrolysis is used to extract aluminium but is not used to extract iron. (2)

Answer 43

Iron is higher in the reactivity series/more reactive than carbon/iron is less reactive than carbon (1)
For aluminium, electrolysis is a powerful means of production/needs more energy (1)
For iron, it can be reduced with carbon/use of carbon for extraction is cheaper (1)

Question 44

An alloy of aluminium with magnesium is used for parts of aeroplanes.
Explain why the aluminium alloy is stronger than pure aluminium. (2)

Answer 44

Magnesium and aluminium atoms are different sizes (1)
This prevents the layers of atoms from sliding over each other (1)

Question 45

When aluminium corrodes, it reacts with oxygen to form aluminium oxide, Al2O3.
Balance this equation: (2)
……………. Al + ……………. O2 → 2Al2O3

Answer 45

4Al + 3O2 → 2Al2O3
(2)

Question 46

A student carried out an experiment to see how reactive different metals are when they are placed in dilute hydrochloric acid.
A sample of each metal was placed in a separate test tube of acid.
When zinc reacts with dilute hydrochloric acid, a gas is given off and zinc chloride is formed.
Which gas is given off? (1)
A carbon dioxide
B chlorine
C hydrogen
D oxygen

Answer 46

hydrogen

Question 47

What is the formula of zinc chloride? (1)

Answer 47

ZnCl2

Question 48

A student carried out an experiment to see how reactive different metals are when they are placed in dilute hydrochloric acid.
A sample of each metal was placed in a separate test tube of acid.
The student used the same amount of each metal in a finely powdered form.
State two factors, concerning the hydrochloric acid, which should also be controlled to produce valid results. (2)

Answer 48

Volume (1)
Concentration (1)
Temperature (1)

Question 49

Explain why aluminium is extracted by a different method rather than heating the ore with carbon. (2)

Answer 49

Aluminium compounds are more stable than iron compounds (1)
So carbon is not a strong enough reducing agent to produce aluminium from its ore (1)

Question 50

The extraction of iron involves the reduction of iron oxide, Fe2O3, by carbon monoxide, CO. During this reaction, the iron oxide is reduced to iron, Fe, and the carbon monoxide is oxidised to carbon dioxide. Write the balanced equation for the reaction. (2)

Answer 50

Fe2O3 + 3CO → 2Fe + 3CO2
(2)

Question 51

Iron is extracted from iron oxide, Fe2O3.
In the extraction process the iron oxide is heated with carbon to form iron and carbon dioxide.
Write the balanced equation for this reaction. (3)

Answer 51

2Fe2O3 + 3C → 4Fe + 3CO2
(3)

Question 52

Pure metal can be converted into alloys.
In many cases alloys are more useful than pure metals, for example they are stronger. Gold alloys, stainless steel and nitinol are examples of useful alloys.
Describe how alloying improves the usefulness of metals and how strength is increased in terms of structure. (6)

Answer 52

Property change (other than increased strength) or use of alloy
• increased hardness
• decreased malleability
• increased corrosion resistance
• shape-memory
• gold alloy for jewellery
• stainless steel used for cutlery
• steel used for construction
• nitinol (shape-memory alloy) used for spectacle frames / stents
• idea of any use of metal after alloying

Structural change
• pure metal - atoms are all the same size / suitable diagram of pure metal structure
• atoms arranged in a regular way / lattice
• alloy - atoms are of different sizes / suitable diagram of alloy structure
• disrupts arrangement of atoms
• atoms in pure metal structure can slide over each (when bent)
• alloy - sliding prevented by different sized atoms

Question 53

In the extraction of tin from tin oxide, tin oxide is heated with carbon. SnO2 + C → Sn + CO2
When the tin oxide reacts with carbon to form the products (1)
A tin is oxidised
B tin oxide is reduced
C carbon is reduced
D carbon dioxide is oxidised

Answer 53

tin oxide is reduced

Question 54

Pure gold is too soft to be used for some jewellery.
Gold alloys contain other metals such as copper and silver.
In terms of the arrangement of metal atoms, explain why gold alloys are stronger than pure gold. (2)

Answer 54

Alloys have different sized atoms (1)
Atoms/layers slide over each other easily in pure metals (1)
Structure/layers disrupted in alloy (1)
Stops atoms/layers sliding over each other easily (1)

Question 55

Metals are obtained from the Earth’s crust by different methods.
Some metals are found uncombined but others have to be extracted from their ores by electrolysis or by heating the ore with carbon.
Explain, using aluminum, gold and iron as examples, how the method used to obtain the metal is related to its position in the reactivity series and to the cost of the extraction process. (6)

Answer 55

gold:
• gold is an unreactive metal/at the bottom of the reactivity series
• it does not combine with other elements in the Earth’s crust
• so is found as uncombined metal
• cost of recovery is low
iron:
• iron is a more reactive metal than gold and less reactive than aluminium/middle of reactivity series
• found combined with other elements
• it is extracted by heating with carbon
• electrolysis can be used
• but electrolysis is more expensive (than heating with carbon)
aluminium:
• aluminium is a very reactive metal/near to top of the reactivity series
• found combined with other elements
• it is extracted by electrolysis
• because it is very difficult to reduce
• electrolysis is a powerful method of reduction • use of electricity makes this method expensive

Question 56

Sulfur trioxide is produced by reacting sulfur dioxide with oxygen.
2SO2 + O2 ↔️ 2SO3
This reaction takes place in industry at 1–2 atm pressure and can reach a dynamic equilibrium.
Explain the effect on the rate of attainment of equilibrium, if the process is carried out at a pressure higher than 1–2 atm. (3)

Answer 56

Rate increased (1)
Because gas molecules closer (1)
So increased collision rate/more frequent collisions(1)

Question 57

When there are alternative methods of producing a product, the final pathway is chosen by considering atom economy, cost of energy, yield of product and rates of reactions.
State another factor that should also be considered. (1)

Answer 57

Equilibrium position/usefullness of products

Question 58

The reaction between nitrogen and hydrogen is exothermic.
N2 + 3H2 ↔️ 2NH3
If nitrogen and hydrogen were reacted at 150 atm pressure and 300 °C, without a catalyst, some ammonia would be formed.
In the Haber process a pressure of 150 atm and a temperature of 450 °C are used, in the presence of an iron catalyst.
Explain why the conditions used in the Haber process are better than the first set of
conditions for the manufacture of ammonia. (6)

Answer 58

• higher temperature reaches equilibrium faster because molecules move faster
• therefore there are more frequent collisions because molecules have more energy
• therefore more collisions have required energy but yield will be lower
• because higher temperature favours endothermic reaction and so equilibrium shifts to left hand side
• which is decomposition of ammonia/ammonia reforms elements
• catalyst causes reaction to reach equilibrium faster / catalyst increases rates (of both forward and back reactions)
• lowers the activation energy (of both forward and back reactions) but does not affect yield
• equilibrium position not affected.