GCSEChemistry: Combined ScienceEdexcelExam Questions4. Extracting Metals & Equilibria4.2 Reversible Reactions & Equilibria

Reversible Reactions & Equilibria (Edexcel GCSE Chemistry: Combined Science)

Exam Questions

35 mins11 questions
Medium
Hard
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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16 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.

(6)

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26 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.

(6)

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