Equilibria (OCR GCSE Chemistry A (Gateway))

Exam Questions

34 mins20 questions
1a2 marks

The reversible reaction between carbon dioxide and hydrogen makes methane and water.

carbon dioxide + hydrogen ⇌ methane + water

In a sealed container, this reversible reaction forms a dynamic equilibrium.

What is meant by the term dynamic equilibrium?

Refer to both concentration and rate of reaction in your answer.

1b
Sme Calculator
2 marks

A student investigates this reaction between carbon dioxide and hydrogen.

He predicts that 11.0 g of carbon dioxide should make 4.0 g of methane.

In an experiment, he finds that 11.0 g of carbon dioxide makes 2.2 g of methane.

Calculate the percentage yield of methane.

 

Answer = ………………………………… %

1c6 marks

Higher Only

The student investigates the effect of changing pressure and changing temperature on this reaction.

carbon dioxide + hydrogen ⇌ methane + water

The table shows the percentage yield of methane in the equilibrium mixture under different conditions.

Temperature (in oC)

 

Pressure (in atmospheres)

 

100

200

300

400

300

35%

52%

65%

80%

600

30%

46%

58%

74%

900

23%

37%

47%

62%

1200

14%

25%

36%

48%

Describe what happens to the percentage yield as the pressure and temperature change and explain the effect of increasing the pressure on the rate of reaction.

Did this page help you?

26 marks

Higher Only

Ethanol is manufactured by reacting ethene, C2H4, with steam.

The reaction is reversible and occurs in a closed system.

C2H4 (g) + H2O (g) ⇌ C2H5OH (g)  ΔH = – 45 kJ mol–1

Only 5% of the ethene is converted into ethanol at each pass through the reactor.

By removing the ethanol from the equilibrium mixture and recycling the ethene, it is possible to achieve an overall 95% conversion.

q19-paper-4-june-2018-ocr-gcse-chem

Explain why the conditions used for the process are chosen.

Did this page help you?