Edexcel GCSE Chemistry

Topic Questions

GCSEChemistryEdexcelTopic Questions4. Extracting metals & equilibria4.2 Reversible Reactions & Equilibria

4.2 Reversible Reactions & Equilibria

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1a1 mark

Ammonia can be made from nitrogen and hydrogen during the Haber process.  The forward reaction is exothermic.

nitrogen + hydrogen     rightwards harpoon over leftwards harpoon      ammonia 


What does therightwards harpoon over leftwards harpoon symbol mean?

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1b2 marks

Complete the balanced symbol equation for the reaction.


___ N2 + ___ H2rightwards harpoon over leftwards harpoon ___ NH3

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1c2 marks

Draw one straight line from each raw material used in the Haber process to where it is obtained from

haber-process-match-up

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1d1 mark

Higher Only

Which statement about the Haber process is true?

  ☐ A A pressure of 450 atmospheres is used
  ☐ B Copper is used as a catalyst
  ☐ C A higher yield of ammonia is obtained at lower temperatures
  ☐ D A higher yield of ammonia is obtained at lower pressures

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2a2 marks

The reaction between nitrogen and hydrogen to produce ammonia can reach a dynamic equilibrium. 

N2 + 3H2  rightwards harpoon over leftwards harpoon 2NH3

Here are five statements about dynamic equilibrium. 

Place ticks in boxes by the two statements that are correct. 

The position of equilibrium cannot be changed   
The concentrations of the reactants and products are equal  
 The rate of the forward and reverse reactions are equal  
 A catalyst is needed to help establish a dynamic equilibrium  
The concentration of reactants and products remains unchanged  

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2b3 marks

Give the reaction conditions for the Haber process:

Temperature ..............
Pressure ..............
Catalyst ..............

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2c3 marks

Higher Only

Use words from the box to complete the sentences to explain the effect of increasing pressure on the yield of ammonia. 

increase decrease forward
fewer reverse more  


Increasing pressure will cause the rate of the ________ reaction to increase. 

This is because there are _______ molecules on the right hand side which will reduce the pressure. 

The yield of ammonia will __________. 

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2d1 mark

The Haber process is exothermic. 

What is meant by an exothermic reaction?

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3a1 mark

Ammonium chloride is a white solid. It breaks down when heated, forming ammonia and hydrogen chloride. When these two gases are cool enough, they react together to form ammonium chloride again.

The word equation for the reaction is:

ammonium chloride ⇌ ammonia + hydrogen chloride

The reaction has a forward reaction and a backward reaction that take place at the same time.

Give the name of this type of reaction.

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3b1 mark

Which row in the table correctly shows the type of reaction happening in the forward and backward reaction?

 

 

 Forward reaction Backward reaction
☐ A Endothermic Endothermic
☐ B Endothermic Exothermic
☐ C Exothermic Endothermic
☐ D Exothermic Exothermic

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3c1 mark

The symbol equation for the reaction is:

NH4Cl (s) ⇌ NH3 (g) + HCl (g)

Write the symbol equation for the backward reaction.

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3d1 mark

A teacher heats some ammonium chloride in a test tube.
A white powder forms at the top of the test tube.

Name the white powder.

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4a1 mark

Sulfur reacts with oxygen to form sulfur trioxide in a reversible reaction:

sulfur + oxygen ⇌ sulfur trioxide

How does the word equation show this is a reversible reaction?

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4b1 mark

Complete the balanced symbol equation for the reaction:

2SO2 (g) + O2 (g) ⇌ ………SO3 (g)

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4c2 marks

The reaction can reach a dynamic equilibrium.

Use words from the box to complete the sentences about dynamic equilibrium.

       different                 equal                     pressure                      rate                  temperature      

In a dynamic equilibrium the ………………. of the forward reaction and the backwards reaction are ………………

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4d2 marks

The reaction happens at a pressure of 2 atmospheres. Another unit of pressure is Pascals, Pa (1 atmosphere = 101 325 Pa).

Calculate the value of 2 atmospheres in Pascals.

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5a1 mark

A teacher puts some hydrated copper sulfate (CuSO4.5H2O) into a test tube and gently heats the bottom.
Hydrated copper sulfate is a blue solid.
When it is heated it breaks down to form anhydrous copper sulfate (CuSO4) and water (H2O)
Anhydrous copper sulfate is a white solid.

This is a reversible reaction.

Write the word equation for this reaction.

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5b1 mark

As the hydrated copper sulfate is heated it goes white.

Give one other change the teacher would observe.

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5c1 mark

The teacher leaves the tube to cool.
She then adds a few drops of water to the test tube.

Predict what colour the white powder will turn.

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5d1 mark

Predict how the temperature inside the test tube will change.

Give a reason for your answer.

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1a
Sme Calculator1 mark

Higher Only

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.

2 SO subscript 2 space open parentheses straight g close parentheses space plus space straight O subscript 2 space open parentheses straight g close parentheses space stack rightwards harpoon over leftwards harpoon space 2 SO subscript 3 space end subscript with blank below and blank on top open parentheses straight g close parentheses

What volume of sulfur trioxide, in dm3, is produced by the complete reaction of 750 dm3 of sulfur dioxide?
(all volumes of gases are measured under the same conditions of temperature and pressure)
 
  ☐ A 375.5
  ☐ B 750
  ☐ C 1125.5
  ☐ D 1500

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1b
Sme Calculator1 mark

Higher Only

Calculate the volume of oxygen needed to react completely with 750 dm3 of sulfur dioxide.
(all volumes of gases are measured under the same conditions of temperature and pressure)

volume of oxygen = .............................. dm3

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1c
Sme Calculator3 marks

Higher Only

Calculate the mass, in kilograms, of 750 dm3 of sulfur dioxide, measured at room temperature and pressure.
(relative formula mass: SO2 = 64;
1 mol of any gas at room temperature and pressure occupies 24 dm3)

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1d6 marks

Higher Only

The reaction to produce sulfur trioxide reaches an equilibrium.

 
2SO2 (g) + O2 (g) rightwards harpoon over leftwards harpoon2SO3 (g) 
 

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 in Figure 7.

set of conditions pressure in atm temperature in °C catalyst
A 2 680 no catalyst used
B 4 425 catalyst used

Figure 7

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 the set of conditions A.

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2a1 mark

Hydrogen-oxygen fuel cells, rather than chemical cells, can be used to power some vehicles.

Give one advantage of using a hydrogen-oxygen fuel cell, rather than using a chemical cell, to power a vehicle.

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2b2 marks

Higher Only

Complete the half-equation for the reaction taking place at one of the electrodes in a hydrogen-oxygen fuel cell.

O2 + .................. H++ .................. → ............... H2O

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2c
Sme Calculator2 marks

Higher Only

Calculate the volume of 48 g of oxygen at room temperature and pressure.

(relative atomic mass: O = 16,1 mol of gas occupies 24 dm3 at room temperature and pressure)

volume of oxygen = ............................................................... dm3

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2d6 marks

Higher Only

The hydrogen used in a hydrogen-oxygen fuel cell can be produced from methanol, CH3OH.

CH3OH + H2O rightwards harpoon over leftwards harpoon for blank of CO2 + 3H2

In this reaction the forward reaction is endothermic and heat energy is taken in from the surroundings.
The conditions used for this reaction 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.

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3a2 marks

Higher Only

Chemistry Only

Ammonia is produced by reacting hydrogen and nitrogen in the Haber process.

N2 (g) + 3H2 (g) ⇌ 2NH3 (g)

The forward reaction is exothermic.
An iron catalyst is used.

State the effect of the iron catalyst on the:

i)
Rate of reaction

[1]

ii)
Equilibrium yield of ammonia

[1]

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3b2 marks

The rate of the reaction increases with temperature.

Explain why.

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3c2 marks

Higher Only

A temperature of 450°C is used, even though a higher temperature would increase the rate of the reaction.

Explain why this temperature is chosen for the reaction.

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3d2 marks

Higher Only

A high pressure of 200 atmospheres is used.

Explain why, in terms of the equilibrium yield of ammonia.

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4a1 mark

Hydrated copper(II) sulfate contains copper(II) sulfate joined with water molecules.

The ratio of water to copper(II) sulfate can vary.

State the formula of the ions in copper(II) sulfate.

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4b4 marks

Higher Only

22.5g of hydrated copper(II) sulfate (CuSO4.XH2O) is heated to form 14.4 g of anhydrous copper(II) sulfate.

Calculate X to deduce the formula of the hydrated copper(II) sulfate.

(relative formula masses:CuSO4 = 159.5; H2O = 18)

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4c2 marks

Heating blue hydrated copper(II) sulfate to form white anhydrous copper(II) sulfate is a reversible reaction.

Devise a way of proving this.

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4d2 marks

Predict how temperature changes when water is added to anhydrous copper sulfate.

Give a reason for your answer.

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5a2 marks

The reaction between hydrogen (H2) and iodine (I2) to form hydrogen iodide is exothermic.

The balanced symbol equation for this reaction is:

H2 (g)+I2 (g) ⇌ 2HI (g)

Draw a dot and cross diagram to show the bonding in a molecule of hydrogen iodide.

Show the electrons on the outer shells only.

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5b3 marks

Higher Only

At a high temperature, an equilibrium mixture of the gases generates a dark purple color.  H2 is colourless.

Which gas is purple: I2 or HI?

Explain your answer.

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5c1 mark

Higher Only

Changing the pressure has no effect on the equilibrium yield of hydrogen iodide.

State why.

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5d1 mark

Higher Only

Explain the effect of increasing the concentration of hydrogen in the reaction mixture on the equilibrium yield of hydrogen iodide.

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1a4 marks

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.

 
CuSO4.5H2O rightwards harpoon over leftwards harpoonCuSO4 + 5H2O 
 

Devise an experiment to show that this is a reversible reaction.

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1b2 marks

Hydrogen reacts with iodine to form hydrogen iodide.
Iodine gas is purple and hydrogen iodide gas is colourless.

 
H2 (g) + I2 (g) rightwards harpoon over leftwards harpoon 2HI (g)
 

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.

 

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1c
Sme Calculator2 marks

Higher Only

Calculate the number of atoms combined in one mole of copper iodide, CuI2.

 
(Avogadro constant = 6.02 × 1023)
 
 
number of atoms = ..............................................................

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21 mark

The Haber process is an example of a reversible reaction where the forward reaction is exothermic:

N2 (g) + 3H2 (g) rightwards harpoon over leftwards harpoon 2NH3 (g)

What is not true about this system when it is at equilibrium?

  ☐ A The energy change of the reverse reaction is endothermic
  ☐ B The equilibrium occurs within a closed system
  ☐ C The reaction has reached completion and stopped
  ☐ D The rate of the forward reaction is equal to the rate of the reverse reaction

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31 mark

Which graph shows the highest yield of products?

  ☐ A graph-a
  ☐ B graph-b
  ☐ C graph-c


☐ D None of the above

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4a4 marks

In industry, ammonia is manufactured by reacting nitrogen with hydrogen.

i)
Give the name of the industrial process used to manufacture ammonia.
(1)
ii)
Write the word equation for this reaction, including the correct symbol to show that the reaction is reversible.
(3)

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4b1 mark

The formula of ammonia is NH3.

State what the formula of ammonia shows about the number of nitrogen atoms and the number of hydrogen atoms combined in a molecule of ammonia.

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4c3 marks

Most of the ammonia manufactured in industry is used to produce fertilisers.

i)
A fertiliser is made by reacting ammonia with nitric acid.

What is the name of this fertiliser?
(1)
  ☐ A ammonia nitrate
  ☐ B ammonia nitric 
  ☐ C ammonium nitrate 
  ☐ D ammonium nitric 

ii)
Explain the importance of fertilisers in farming.
(2)

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51 mark

Which is not true about the Haber process for making ammonia?

  ☐ A Platinum is used as a catalyst
  ☐ B The process is carried out at a temperature if 450 oC
  ☐ C The process takes place at a pressure of about 200 atmospheres
  ☐ D Natural gas is a raw material

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61 mark

What does the graph show about the effect of pressure and temperature on the Haber process?

10-4

  ☐ A Less ammonia is produced at higher pressures
  ☐ B The yield of ammonia decreases with increased temperature
  ☐ C The optimum conditions are low pressure and high temperature
  ☐ D At 500 atmospheres and 400 oC the yield of ammonia is 45%

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71 mark

Higher Only

The decomposition of ammonium chloride is endothermic:

NH4Cl (s) rightwards harpoon over leftwards harpoonNH3 (g) + HCl (g)

Which changes to the conditions would both decrease the amount of product in this reaction?

      Change 1 Change 2
  ☐ A Increase pressure Decrease temperature
  ☐ B Decrease pressure Decrease temperature
  ☐ C Increase pressure Increase temperature
  ☐ D Decrease pressure Increase temperature

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81 mark

Which option shows two correct statements about reversible reactions and equilibrium?

      Statement 1 Statement 2



☐ A The sign for a reversible reaction is rightwards harpoon over leftwards harpoon Reversible reactions are slower than non-reversible ones



☐ B At equilibrium the rate of the forward reaction and the rate of the reverse reaction are equal An endothermic reaction is exothermic if reversed



☐ C Reversible reactions are not useful in industry as they do not go to completion To reach an equilibrium the reaction must occur in a closed system



☐ D The rate of the reaction is zero at equilibrium The concentration of the product is constant at equilibrium

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91 mark

Higher Only

The gasification of carbon is a reversible endothermic reaction:

C (s) + H2O (g) rightwards harpoon over leftwards harpoon CO (g) + H2 (g)

Which of the following conditions could be changed to increase the relative amount of H2 gas produced?

  ☐ A Increase the surface area to volume ratio of the carbon
  ☐ B Increase the pressure
  ☐ C Increase the temperature
  ☐ D Add a catalyst

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