Dynamic equilibrium

Sulfuric acid is produced by an industrial process.

In the process, sulfur dioxide (SO₂) reacts with oxygen (O₂) to produce

The equation for the reversible reaction is:

The forward reaction releases 198 kJ/mol of energy.

What is the amount of energy transferred during the reverse reaction?

Tick () one box.

The concentration of oxygen is increased.

What is the effect on the position of the equilibrium?

Tick () one box.

The pressure is decreased.

What is the effect on the position of the equilibrium?

Tick () one box.

The temperature is increased.

What is the effect on the position of the equilibrium?

Tick () one box.

A catalyst is used in the reaction.

Suggest what effect the catalyst has on the position of the equilibrium.

Give one reason for your answer.

A scientist measured how the number of moles of sulfur dioxide, oxygen and

sulfur trioxide varied with time during the reaction.

Figure 5 shows the results.

Determine the time taken for the reaction to reach equilibrium.

Explain your answer.

Use Figure 5.

Figure 6 shows the results for sulfur trioxide.

Determine the rate of reaction at 60 seconds.

Some types of water contain dissolved substances.

A student investigated the mass of dissolved solids in distilled water and in sea water. Figure 5 shows the apparatus.

This is the method used.

1. Weigh an evaporating basin.

2. Add a sample of distilled water to the evaporating basin.

3. Weigh the evaporating basin and the water sample.

4. Heat the water sample.

5. Weigh the evaporating basin and contents.

6. Repeat steps 1 to 5 two more times.

7. Repeat steps 1 to 6 with sea water.

Give one safety precaution the student should take.

The method used did not give valid results. Which two improvements could the student make to give valid results? Tick (✓) two boxes.

A different student used a method which gave valid results. Table 2 shows the results.

The student concludes that distilled water is pure. Suggest one reason why.

Tap water is potable. One step in producing potable water is sterilisation.

Why is potable water sterilised?

Tick (✓) one box.

Chlorine is used to sterilise water. The reaction between chlorine and water is reversible. Complete the sentence.

Equilibrium is reached when the forward and reverse reactions

The test for chlorine uses damp litmus paper. Complete the sentence. Choose the answer from the box.

When damp litmus paper is put into chlorine gas

There is evidence that adding fluoride ions to drinking water reduces tooth decay.

Figure 6 shows the percentage of people showing tooth decay.

Compare the effects of adding fluoride ions to drinking water on tooth decay in people between the ages of 25 and 74. Use data from Figure 6.

Student A says that water companies should add fluoride ions to all drinking water. Student B disagrees. Suggest one reason why Student B may think that fluoride ions should not be added to all drinking water.

Some types of water contain dissolved substances.

A student investigated the mass of dissolved solids in distilled water and in sea water. Figure 1 shows the apparatus.

This is the method used.

1. Weigh an evaporating basin.

2. Add 20 cm³ of distilled water to the evaporating basin.

3. Weigh the evaporating basin and the water sample.

4. Heat the water sample for 2 minutes.

5. Weigh the evaporating basin and contents.

6. Repeat steps 1 to 5 two more times.

7. Repeat steps 1 to 6 with sea water.

The method used by the student did not give valid results. Describe one improvement the student could make to obtain valid results.

A different student used a method which gave valid results.

Table 2 shows the results.

Calculate the value X for the mass of dissolved solids in sea water in Test 2.

The student concludes that distilled water is pure. Describe a test to confirm that distilled water is pure.

Tap water is potable.

A stage in the production of potable water is sterilising. A gas is used to sterilise water. The equation for the reaction is:

What is meant by the symbol ?

The reaction is at equilibrium. The reaction is exothermic. What happens to the equilibrium position when the temperature is increased? Tick (✓) one box.

Describe a test to identify the gas used to sterilise water.

Another stage in the production of potable water is filtering. Explain why potable water contains dissolved solids after filtering.

This question is about ammonia and its compounds.

A student heated a sample of ammonium chloride.

The equation for the reaction is:

One product is ammonia.

What is the name of the product with the formula HC l ?

Ammonia is a gas.

What is the state symbol for ammonia?

Tick (✓) one box.

How does the equation show that the reaction is reversible?

The industrial process to produce ammonia uses a catalyst.

Figure 5 shows the reaction profile for the reaction with and without a catalyst.

Which letter represents the activation energy for the reaction with a catalyst?

Tick (✓) one box.

Give one reason why using a catalyst reduces costs.

Do not answer in terms of activation energy.

Ammonia is in a mixture that is used as a household cleaner.

What is a mixture that has been designed as a useful product called?

This question is about catalysts and equilibrium.

What type of substance is a catalyst in biological systems? Tick (✓) one box.

Explain how a catalyst increases the rate of a reaction.

The reversible reaction for the production of ammonia is:

What can scientists predict using Le Chatelier’s Principle?

Describe how a reversible chemical reaction is able to reach equilibrium.

Explain the effect of increasing the pressure on the yield of ammonia.

The forward reaction to produce ammonia is exothermic. Explain the effect of increasing the temperature on the yield of ammonia.

Ammonia is produced when a mixture of nitrogen and hydrogen reacts.

The equation for the reaction is:

Nitrogen is obtained from the air.

The mixture of nitrogen and hydrogen must not contain carbon dioxide and oxygen.

Explain how a sample can be tested to show that carbon dioxide is not present in the mixture.

A catalyst is used in the reaction.

Explain how a catalyst increases the rate of a reaction.

The equation for the reaction to produce ammonia is repeated here.

The reaction reaches equilibrium.

Explain how an equilibrium is reached.

Suggest how the catalyst affects the equilibrium position.

Give one reason for your answer.

What is the effect of increasing the pressure on the reaction to produce ammonia?

Tick (✓) one box.

The forward reaction is exothermic.

Explain the effect of increasing the temperature on the yield of ammonia gas produced at equilibrium.

This question is about equilibrium.

Describe how a reaction reaches equilibrium.

Nitrogen dioxide gas reacts to form dinitrogen tetraoxide gas. The reaction is reversible. The equation for the reaction is:

Explain the effect on the equilibrium position of increasing the pressure.

Figure 7 shows the change in the percentage of dinitrogen tetroxide (N₂O₄) in the equilibrium mixture as the temperature of the equilibrium mixture is changed.

Explain the effect on the equilibrium position of increasing the temperature. Use Figure 7.

This question is about gases.

Draw one line from each substance to the description of the substance.

What is used to test for each of the gases?

Draw one line from each gas to the test for the gas.

Give two reasons why the percentage of carbon dioxide in the air has decreased in the last 2.7 billion years.

Tick (✓) two boxes.

Oxygen reacts with sulfur dioxide.

The reaction is reversible.

What is the symbol for a reversible reaction?

Complete the sentence.

In a reversible reaction the forward reaction is exothermic, so the

A reversible reaction happens in apparatus which stops the escape of reactants and products.

Complete the sentence.

Equilibrium is reached when the forward and reverse reactions happen at

What percentage of the Earth’s atmosphere is nitrogen?

Tick one box.

During the first billion years of the Earth’s existence the amount of nitrogen in the atmosphere increased.

Give one source of this nitrogen.

Nitrogen is used to make ammonia.

The word equation for the reaction is:

Write the correct symbol in the equation to show that it is a reversible reaction.

A reversible reaction can reach equilibrium.

Complete the sentence.

Equilibrium is reached when the forward reaction and the reverse reaction happen at

Fertilisers are formulations containing nitrogen.

What is a formulation?

Table 4 shows percentages of chemical elements in a fertiliser.

Draw the bar for potassium on Figure 8

Use the information in Table 4

A fertiliser contains 0.225 g of iron per 3.0 g of fertiliser.

Which calculation gives the percentage of iron in the fertiliser?

Tick one box.

Figure 9 shows the use of fertiliser in four different countries, A, B, C and D, in 2003 and 2015

A student said:

‘ much more fertiliser was used in 2015 than in 2003’

Is the student correct?

Use data from Figure 9 to justify your answer.

Bleach is a solution of sodium hypochlorite (NaClO). Chlorine gas is produced when bleach reacts with hydrochloric acid. NaClO(aq) + 2HCl (aq) NaCl(aq) + H₂O(l) + Cl₂(g)

Give the test and result for chlorine gas.

Figure 8 shows a sealed flask of sodium hypochlorite and hydrochloric acid at equilibrium.

Explain why equilibrium is reached in this reaction.

The stopper in Figure 8 is removed and hydrochloric acid is added. The stopper is replaced. Explain what happens to the equilibrium.

Chlorine gas is also produced when hydrogen chloride decomposes.

The forward reaction is endothermic.

Predict the effect of increasing the temperature on the amount of chlorine gas produced at equilibrium. Explain your answer using Le Chatelier’s Principle.

Explain the effect of increasing the pressure on this equilibrium.