GCSE Chemistry Equilibrium questions by topic

This question is about reversible reactions.

1. (a)State what is meant by a reversible reaction.[1]
2. (b)State two features of a reaction mixture at dynamic equilibrium.[2]

Hydrated copper(II) sulfate is heated in a test tube.

1. (a)State the colour change seen.[1]
2. (b)Write the word equation for adding water to the product.[1]
3. (c)Explain why the reverse change cannot happen if the tube is left open.[1]

28 g of nitrogen reacts with excess hydrogen. The equation is N₂ + 3H₂ ⇌ 2NH₃. The run produces 25.5 g of ammonia. (Mr: N₂ = 28, NH₃ = 17)

1. (a)Calculate the theoretical yield of ammonia.[2]
2. (b)Calculate the percentage yield.[2]

This question is about the Haber process.

1. (a)Name the catalyst used.[1]
2. (b)State the temperature and pressure used.[2]
3. (c)State why the ammonia is cooled on leaving the reactor.[1]

Complete the sentences about reversible reactions and equilibrium.

1. (a)At dynamic equilibrium the forward and reverse reactions happen at the … rate.[1]
2. (b)Dynamic equilibrium can only be reached in a … system.[1]
3. (c)Hydrated copper(II) sulfate is … in colour; anhydrous copper(II) sulfate is … .[1]
4. (d)State what Le Chatelier’s principle predicts after a change in conditions.[1]
5. (e)Write the symbol used in an equation to show a reversible reaction.[1]

A student adds a few drops of water to white anhydrous copper(II) sulfate in a polystyrene cup: the powder turns blue and the temperature rises from 19.8 °C to 24.6 °C.

1. (a)Calculate the temperature rise and state whether the hydration is exothermic or endothermic.[2]
2. (b)Describe the colour change of the reverse reaction and name the technique used to bring it about.[2]
3. (c)State one use of this reversible colour change in the laboratory.[1]

This question is about predicting equilibrium shifts.

1. (a)State Le Chatelier’s principle.[2]
2. (b)Predict the effect of increasing the pressure on 2SO₂(g) + O₂(g) ⇌ 2SO₃(g).[1]
3. (c)Predict the effect of increasing the temperature when the forward reaction is exothermic.[1]

Ammonia is used to make fertiliser salts.

1. (a)Write the equation for ammonia neutralising nitric acid.[2]
2. (b)Name the salt and the nutrient it supplies.[2]
3. (c)State why the salt must be soluble.[1]

Limestone decomposes in a lime kiln: CaCO₃(s) → CaO(s) + CO₂(g). (Mr: CaCO₃ = 100, CaO = 56, CO₂ = 44)

1. (a)Calculate the atom economy of the reaction with respect to calcium oxide.[3]
2. (b)Explain why the atom economy cannot be 100%.[1]
3. (c)Give one use for the co-product and name the industry that uses it.[2]

A and B react reversibly to form C in a sealed container: A + B ⇌ C. Describe what happens from the moment of mixing until equilibrium, in terms of rates.

1. (a)Describe how the forward rate changes.[2]
2. (b)Describe how the reverse rate changes.[2]
3. (c)State the two conditions true at equilibrium.[2]

The Haber equilibrium is N₂(g) + 3H₂(g) ⇌ 2NH₃(g), with an exothermic forward reaction. Complete the table describing each change.

1. (a)Direction of shift when the pressure is increased.[1]
2. (b)Effect on the ammonia yield when the pressure is increased.[1]
3. (c)Direction of shift when the temperature is lowered.[1]
4. (d)Effect on the ammonia yield when the temperature is lowered.[1]
5. (e)Direction of shift when ammonia is removed as it forms.[1]
6. (f)Effect on the ammonia collected per pass when ammonia is removed as it forms.[1]

A fertiliser plant expects a theoretical ammonium nitrate output of 8.0 tonnes from a batch, but obtains 6.8 tonnes.

1. (a)Calculate the percentage yield.[2]
2. (b)Give two reasons why the actual yield is below the theoretical value.[2]
3. (c)The reaction is neutralisation, which goes to completion. Explain why even a complete reaction can still give less than the theoretical yield.[2]

The Haber equilibrium N₂ + 3H₂ ⇌ 2NH₃ has an exothermic forward reaction. Typical equilibrium yields are 60% at 300 °C, 40% at 350 °C, 25% at 400 °C and 16% at 450 °C (at constant pressure).

1. (a)Describe the trend in the data.[1]
2. (b)Explain the trend using Le Chatelier’s principle.[3]
3. (c)Explain why the process nevertheless runs at about 450 °C rather than 300 °C.[3]

A student says: “Adding more iron catalyst will increase the amount of ammonia the plant produces at equilibrium.”

1. (a)Identify the error in the student’s claim.[2]
2. (b)State what the catalyst actually does, and why the plant still buys them.[2]
3. (c)Name one change that would increase the equilibrium amount of ammonia and explain why it works.[2]

Evaluate the operating choices of an ammonia plant.

1. (a)Give two reasons the pressure is kept near 200 atm rather than raised to 1000 atm.[2]
2. (b)Explain why unreacted nitrogen and hydrogen are recycled.[2]
3. (c)State the property of ammonia that lets it be separated from the loop by cooling.[1]
4. (d)Explain the effect on the equilibrium yield of continuously removing ammonia from the reacting mixture.[3]

This question is about NPK fertiliser manufacture.

1. (a)State what is meant by a formulation.[1]
2. (b)Explain why phosphate rock must be treated with acid before use in fertiliser.[2]
3. (c)Give two differences between laboratory and industrial production of a fertiliser salt such as ammonium sulfate.[2]

A chemist explains the Haber operating conditions step by step for a report: N₂(g) + 3H₂(g) ⇌ 2NH₃(g), ΔH = −92 kJ/mol.

1. (a)Explain, in terms of moles of gas, why raising the pressure increases the equilibrium yield.[2]
2. (b)Explain why a low temperature would raise the yield yet is not used.[2]
3. (c)Explain why the iron catalyst changes neither the yield nor the position of equilibrium.[2]
4. (d)State the compromise temperature used and the reason for it.[1]

Ethene reacts with steam to make ethanol: C₂H₄ + H₂O → C₂H₅OH (C 12, H 1, O 16).

1. (a)Calculate the Mr of ethanol and the atom economy of this process.[2]
2. (b)Explain why the atom economy has the value it does.[2]
3. (c)A plant predicts 10.0 tonnes of ethanol from a batch but collects 8.5 tonnes. Calculate the percentage yield.[2]
4. (d)Give two reasons why the collected mass falls short even though the reaction is efficient.[2]