AQA GCSE Chemistry: Combined Science

Topic Questions

GCSEChemistry: Combined ScienceAQATopic Questions6. Chemical Change: Rate & Extent6.2 Reversibility & Equilibrium

6.2 Reversibility & Equilibrium

DownloadView
Easy
Medium
Hard
Easy
Medium
Hard
1a1 mark

When solid ammonium chloride is heated, ammonia gas and hydrogen chloride gas are produced.

The equation for this reaction is:

ammonium chloride rightwards harpoon over leftwards harpoon ammonia + hydrogen chloride

What does the symbol rightwards harpoon over leftwards harpoon mean?

How did you do?

1b1 mark

What type of reaction is the reaction in part (a)?

Tick (✓) one box.

Neutralisation  
Combustion  
Thermal decomposition  
Reduction  

How did you do?

1c1 mark

Circle one word from the box to complete the sentence.

  The reaction can be reversed by

heating it.

cooling it.

adding water.

How did you do?

1d2 marks

The balanced symbol equation is shown below.

Complete the equation by adding the correct state symbols.

NH4Cl ____ rightwards harpoon over leftwards harpoon   NH3 ____   + HCl ____

How did you do?

Did this page help you?

2a2 marks

Hydrated copper sulfate is a blue salt that contains water molecules within its lattice structure.

When heated, the water is removed from the structure, forming white anhydrous copper sulfate.

Complete the word equation for the reaction.

hydrated copper sulfate   rightwards harpoon over leftwards harpoon   ____________________   +   ____________________

How did you do?

2b2 marks

A student heated hydrated copper sulfate using the equipment in Figure 1.

Figure 1

aqa-gcse-6-2e-tq2b-hydrated-copper-sulfate

What two observations would be made when hydrated copper sulfate was heated?

Tick (✓) two boxes.

Hydrated copper sulfate turns white  
Hydrated copper sulfate turns blue  
Substance A is a colourless liquid   
Substance A is a white solid   
Substance A is a blue solution   

How did you do?

2c1 mark

When hydrated copper sulfate is heated, an endothermic reaction occurs.

What type of reaction occurs when water is added to anhydrous copper sulfate?

How did you do?

2d2 marks

The word equation between anhydrous cobalt chloride and water is shown below.

anhydrous cobalt chloride + water rightwards harpoon over leftwards harpoon hydrated cobalt chloride
(blue)                                             (pink)

What colour change would be seen when hydrated cobalt chloride is heated?

How did you do?

2e
Sme Calculator2 marks

5.2 g of hydrated cobalt chloride was heated in a test tube.

3.0 g of anhydrous cobalt chloride remained after heating.

Calculate the mass of water that was given off in grams.

How did you do?

2f
Sme Calculator3 marks

Calculated the percentage of water contained in 5.2 g of hydrated cobalt chloride.

Give your answer to 2 significant figures.

How did you do?

Did this page help you?

3a1 mark

When a reversible reaction occurs in a closed system, it will reach equilibrium.

What is meant by a closed system?

Tick (✓) one box.

Only gases are allowed to escape  
Energy is unable to escape  
The reactants and products are unable to escape  

How did you do?

3b1 mark

Which of the following statements is true about equilibrium?

Tick (✓) one box.

When equilibrium is reached, the reaction stops  
At equilibrium, the amount of reactants is the same as the amount of products  
At equilibrium, the rate of the forward reaction is equal to the rate of the reverse reaction  
When equilibrium is reached, all of the reactants have been used up  

How did you do?

3c3 marks

Aqueous copper (II) ions can react with chloride ions to form copper chloride.

The reaction is a reversible reaction.

Aquesous copper (II) ions are blue and copper chloride solution is yellow.

copper (II) ions + chloride ions rightwards harpoon over leftwards harpoon copper chloride
blue                                               yellow

When left for a few minutes, the reaction reaches equilibrium.

Complete the sentences using words from the box.

green blue yellow
copper (II) ions chloride ions copper chloride


At equilbirium, the reaction mixture is ____________________ because the reaction mixture contains ____________________  and ____________________ .

How did you do?

3d3 marks

The concentration of copper (II) ions was increased in the reaction in part (c).

Circle one word in each box to complete the sentences.

  The system will respond to   

counteract

maximise

increase

the change.

  The amount of products will  

increase

decrease

remain the same

until equilibrium is reached again.

  The reaction mixture will turn  

green.

yellow.

blue.
 

How did you do?

Did this page help you?

4a2 marks

The reaction between nitrogen and hydrogen to form ammonia is a reversible reaction.

The forward reaction is exothermic.

Complete the word equation for the reaction, including the correct symbol that shows the reaction is reversible.

nitrogen   +   ____________________      _______    ammonia

How did you do?

4b3 marks

Predict what would happen to the amount of ammonia produced when the following change of conditions occur.

Choose a word from the box below to complete the table.

increase decrease remain the same

Change of condition Amount of ammonia produced would:
Increasing concentration of nitrogen  
Increasing the temperature  
Using a catalyst  

How did you do?

4c1 mark

In the reaction in part (a), nitrogen, hydrogen and ammonia are all gases.

In addition to the condition in part (b), what other condition could be changed that may alter the position of equilibrium?

How did you do?

Did this page help you?

5a1 mark

Nitrogen dioxide, NO2, which is a dark brown gas, exists in equilibrium with colourless, gaseous dinitrogen tetroxide, N2O4.

The balanced symbol equation for this reaction is shown below.

2NO2 (g) rightwards harpoon over leftwards harpoon N2O4 (g)
dark brown      colourless

How many atoms of oxygen are there in a molecule of dinitrogen tetroxide?

How did you do?

5b2 marks

When the pressure increases, what happens to the amount of dinitrogen, N2O4, in the reaction mixture?

Choose words from the box to complete the sentence. 

increases remains the same fewer
larger decreases

The amount of dinitrogen tetroxide ____________________ because the equilibrium position will shift towards the side with ____________________ number of molecules.

How did you do?

5c1 mark

What would you expect to happen to the colour of the reaction mixture if the pressure was increased?

Circle the correct answer.

Become paler Become darker Remain the same colour

How did you do?

Did this page help you?

1a1 mark

This question is about equilibrium. 

An ionic equation for the reaction between iron (III), Fe3+ and thiocyanate ions, SCN2+ is shown below: 

At room temperature, the mixture of the equilibrium solution is orange. 

   Fe3+ (aq)      +    SCN- (aq)       ⇌  FeSCN2+ (aq)
Colour of solution   yellow colourless       red

Which solvent would be used to dissolve the ions in this reaction?

How did you do?

1b3 marks

Explain the effect, if any, of changing pressure on the colour of the equilibrium mixture. 

How did you do?

1c3 marks

A few drops of a colourless solution containing a high concentration of Fe3+ ions are added to the orange equilibrium mixture.

Explain the colour change observed.

How did you do?

1d3 marks

A water bath is set up at a temperature below room temperature.

When a test tube containing the orange equilibrium mixture is placed in the water bath, the mixture becomes more red.

Explain what this shows about the energy change for the forward reaction.

How did you do?

Did this page help you?

2a2 marks

This question is about reversible reactions.

The decomposition of hydrogen iodide into hydrogen and iodine is reversible.

2HI (g)          H2 (g)     +     I2 (g)

The forward reaction is endothermic. 

Explain the effect of increasing temperature on the amount of hydrogen iodide, HI. 

How did you do?

2b2 marks

Suggest what effect, if any, increasing the pressure will have on the amount of hydrogen iodide at equilibrium.

Give a reason for your answer.

How did you do?

2c2 marks

An endothermic reaction can be represented using the following reaction profile in Figure 1. 

Label

  • Activation energy
  • Overall energy change

Figure 1

aqa-gcse-6-2h-tq-2c-reaction-profile-hydrogen-iodide

How did you do?

2d1 mark

How does the diagram show that the reaction is endothermic?

How did you do?

Did this page help you?

3a2 marks

Methanol, CH3OH, is a fuel that can be produced from carbon monoxide and hydrogen. 

Complete the dot and cross diagram to show the bonding in methanol. 

aqa-gcse-6-2h-tq-3a-methanol-dot-and-cross-diagram

How did you do?

3b1 mark

The reaction between carbon monoxide and hydrogen to produce methanol is shown below. 

The forward reaction is exothermic. 

CO(g)          +          2H2(g)      rightwards harpoon over leftwards harpoon       CH3OH(g)

Explain why the highest equilibrium yield of methanol is obtained at high pressure. 

How did you do?

3c3 marks

Methanol can undergo combustion to release energy. 

The equation for this reaction is shown below:

aqa-gcse-6-2h-tq-3d-combustion-of-methanol-equation


Bond energies are shown in Table 1. 

Table 1. 
  C-H C-O O=O C=O O-H

Bond energy in kJ / mol

 410 360 496 800 466


Calculate the overall energy change for the reaction using the diagram and table above. 

How did you do?

3d2 marks

A catalyst is used in the reaction to produce methanol to increase the rate of the reaction. 

Explain how it increases the rate of reaction. 

How did you do?

Did this page help you?

4a6 marks

Ammonia is produced from the reaction of nitrogen with hydrogen in the Haber process:

N2 (g) + 3H2 (g)   ⇌    2NH3 (g)

The forward reaction is exothermic.

The conditions normally used in the Haber process are:

  • 450 oC
  • Pressure of 200 atm
  • Iron catalyst

Use your knowledge of reversible reactions and the equation to explain why these conditions are used.

To gain full marks you must consider both rate of reaction and yield in your answer.

How did you do?

4b4 marks

Hydrogen can be manufactured on an industrial scale by reacting methane with steam. 

CH4 (g)   +   H2O (g)   rightwards harpoon over leftwards harpoon   CO (g)   +   3 H2   (g)

The forward reaction is endothermic. 

Give the conditions of temperature and pressure that would give the maximum yield of hydrogen. 

How did you do?

4c1 mark

Give one hazard associated with this reaction. 

How did you do?

Did this page help you?

1a4 marks

A company manufactures ethanol (C2H5OH) for sale to other chemical companies as a raw ingredient for many products.

The reaction for the process is as follows:

C2H4 (g) + H2O (g)    ⇌    C2H5OH (g)            

The forward reaction is exothermic.

The temperature and pressure of the reaction can be adjusted to increase the yield of ethanol when the reaction is at equilibrium.

Explain what is meant by the term equilibrium.

How did you do?

1b4 marks

Explain what effect increasing the temperature would have on the yield of ethanol at equilibrium.

How did you do?

1c2 marks

Explain what effect increasing the pressure would have on the yield of ethanol at equilibrium.

How did you do?

1d2 marks

How can the direction of a reversible reaction be changed?

How did you do?

1e6 marks

Figure 1 shows the effect of changing pressure on the percentage yield of ethanol at three different temperatures.

Figure 1

6-2-reversibility--equilibrium-medium-q1e-fig1

Figure 2 shows the effect of changing temperature on the rate of reaction at three different pressures.

Figure 2

6-2-reversibility--equilibrium-medium-q1e-fig2

The conditions for the reaction of ethene with steam in one of the processes are: 

  • 65 atm
  • 300 oC
  • a catalyst.

Use your knowledge and the information in Figure 1 and Figure 2 to justify this choice of conditions.

How did you do?

Did this page help you?

2a2 marks

This question is about chemical equilibrium and reversible reactions.

If carried out in a closed system, reversible reactions can reach a state of equilibrium. 

Explain what a closed system is.

How did you do?

2b2 marks

When a reversible reaction reaches equilibrium, it appears to have stopped. 

Explain why.

How did you do?

2c4 marks

In the Haber process, the reaction of nitrogen with hydrogen to produce ammonia is reversible.

N2 (g)     +     3H2 (g)     ⇌      2NH3 (g)

Explain, with reasons, what happens to the amount of ammonia produced at equilibrium if the pressure is increased.

How did you do?

Did this page help you?

3a4 marks

Methanol is produced by reacting carbon monoxide with hydrogen as shown in the equation:

CO (g) + 2H2 (g)   ⇌   CH3OH (g)

The reaction is normally performed at a temperature of 250 °C and a pressure of 100 atm.

The forward reaction is exothermic.

Explain what would happen to the yield of methanol if a temperature higher were used.

How did you do?

3b4 marks

Explain why the high pressure gives a greater yield of methanol and an increased rate of reaction.

How did you do?

Did this page help you?

4a3 marks

A pink coloured compound of cobalt reacts with hydrochloric acid. 

The word equation for the reaction is:

pink cobalt compound + hydrochloric acid ⇌ blue cobalt compound + water

The forward reaction is endothermic. 

If carried out under correct conditions the reaction reaches equilibrium. 

The mixture at equilibrium contains both cobalt compounds and the mixture is purple.

The equilibrium mixture is cooled.

Explain what happens to the concentration of the pink cobalt compound on cooling.

How did you do?

4b2 marks

A chemist adds more hydrochloric acid to the reaction.

Explain what happens to the colour of the mixture.

How did you do?

Did this page help you?