Reversible reactions

Cement, concrete and steel are building materials.

Cement contains calcium oxide.

Calcium oxide reacts with water to produce calcium hydroxide.

The equation for the reaction is:

How does the equation show that this reaction is reversible?

The forward reaction is exothermic.

What type of reaction is the reverse reaction?

When excess water is added to 20 g of calcium oxide, 23 kJ of energy is released.

Calculate the energy released when excess water is added to 4 g of calcium oxide.

Pre-stressed concrete contains steel wires within the concrete.

Figure 2 shows the structure of a piece of pre-stressed concrete.

Pre-stressed concrete is a composite.

Draw one line from each component of a composite to a material in pre-stressed concrete.

Component of composite Material in pre-stressed concrete

Which metal do all steels contain?

Bricks are also building materials.

Bricks are ceramics.

Which material is used to make bricks?

Tick () one box.

This question is about water.

Hydrogen gas reacts with oxygen gas to produce water.

Water is decomposed into hydrogen gas and oxygen gas using electricity.

Which two words describe the reaction between hydrogen gas and oxygen gas?

Tick (✓) two boxes.

Water molecules break down into hydrogen ions and hydroxide ions.

The equation for the reaction is:

Which sentence describes this reaction at equilibrium?

Tick (✓) one box.

Water collected from rivers is used in the home for drinking and flushing toilets.

Water used in the home must be potable.

Potable water is safe to drink.

Waste water produced after use in the home is called sewage.

Figure 12 shows how water is collected from rivers and returned to rivers after use.

Explain what happens to water in Process A and in Process B in Figure 12.

Do not refer to use of water in the home.

This question is about water.

Hydrogen gas reacts with oxygen gas to produce water.

Water is decomposed into hydrogen gas and oxygen gas using electricity.

Which two words describe the reaction between hydrogen gas and oxygen gas?

Tick (✓) two boxes.

Water molecules break down into hydrogen ions and hydroxide ions.

The equation for the reaction is:

Which sentence describes this reaction at equilibrium?

Tick (✓) one box.

Water collected from rivers is used in the home for drinking and flushing toilets.

Water used in the home must be potable.

Potable water is safe to drink.

Waste water produced after use in the home is called sewage.

Figure 3 shows how water is collected from rivers and returned to rivers after use.

Explain what happens to water in Process A and in Process B in Figure 3.

Do not refer to use of water in the home.

This question is about a reversible reaction.

A student heated calcium hydroxide to produce calcium oxide and water vapour.

This is the method used.

1. Add 2.00 g of calcium hydroxide into a test tube.

2. Heat the test tube and contents for 1 minute using a Bunsen burner.

3. Allow the test tube and contents to cool.

4. Weigh the test tube and contents.

5. Repeat steps 2 to 4 five more times.

Table 3 gives the appearance of the reactant and of the products.

The student looked at the test tube and contents during heating.

The student could not tell that a chemical reaction was taking place by looking at the test tube and contents.

Give two reasons why.

Use the information in Table 3.

Accurate results are not produced if solid powders escape from the test tube during heating.

Suggest why sealing the test tube with a stopper is not a good way of preventing the solid powders from escaping.

The student wanted to calculate the mass of the contents of the test tube after each minute of heating.

The student weighed the test tube and contents after each minute of heating.

What other measurement is also needed to calculate the mass of the contents of the test tube?

Tick (✓) one box.

The student heated 2.00 g of calcium hydroxide to produce calcium oxide and water vapour.

Table 4 shows the results.

Complete the sentence.

Choose the answer from the box.

Use Table 4.

The minimum heating time needed for all of the calcium hydroxide to be changed into

Calculate the total mass of water vapour produced by heating the calcium hydroxide.

Use Table 4.

The word equation for the reaction is:

calcium hydroxide calcium oxide + water

The reaction is reversible.

When 4.00 g of calcium hydroxide is completely changed into calcium oxide and water:

• 3.03 g of calcium oxide is produced

• 5.90 kJ of energy is taken in from the surroundings.

3.03 g of calcium oxide reacts completely with water to produce 4.00 g of calcium hydroxide.

How much energy is transferred to the surroundings in this reaction?

Tick (✓) one box.

The forward reaction takes in energy from the surroundings.

Complete the sentence.

Choose the answer from the box.

The forward reaction is.

This question is about reversible reactions.

When 4.68 g of hydrated copper sulfate changes into anhydrous copper sulfate:

• 2.99 g of anhydrous copper sulfate is produced

• 1.47 kJ of energy is taken in from the surroundings.

The equation for the reversible reaction is: hydrated copper sulfate ⇌ anhydrous copper sulfate + water

Calculate the maximum mass of water that can be produced from 11.7 g of hydrated copper sulfate.

15.0 g of anhydrous copper sulfate completely changes into hydrated copper sulfate when water is added.

Calculate the amount of energy transferred to the surroundings.

The gases nitrogen dioxide and dinitrogen tetroxide reach dynamic equilibrium in a sealed container. The equation for the reaction is:

nitrogen dioxide (brown) dinitrogen tetroxide (colourless) The forward reaction is exothermic.

What happens to the position of the equilibrium in this reaction if the temperature is increased?

Tick (✓) one box.

A teacher seals a brown-coloured mixture of nitrogen dioxide and dinitrogen tetroxide in a gas syringe. Figure 8 shows the sealed gas syringe.

Figure 8

The teacher pushes the syringe piston in. This increases the pressure in the gas syringe.

What is the colour of the mixture when a new equilibrium position is reached?

Tick (✓) one box.

Hydrogen iodide gas decomposes into hydrogen gas and iodine gas at high temperatures. The equation for the reaction is:

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

Suggest the effect of adding a catalyst on the equilibrium position of this reaction.

Copper forms coloured compounds. Hydrochloric acid is added to an aqueous solution of copper compound A. The word equation for the reaction is: copper compound A + hydrochloric acid ⇌ copper compound B + water (blue) (yellow)

The reaction mixture is green when both copper compounds are present in a solution at equilibrium. How can the equilibrium position be shifted to make the reaction mixture more yellow?

Tick (✓) one box.

The concentrations of the substances in this reaction do not change at dynamic equilibrium. Explain why.

A student investigated the change in mass when hydrated cobalt chloride was heated. The word equation for the reaction is: hydrated cobalt chloride ⇌ anhydrous cobalt chloride + water

This is the method used.

1. Add 2.0 g of hydrated cobalt chloride to an empty test tube.

2. Measure the mass of the test tube and contents.

3. Heat the test tube and contents gently for 30 seconds.

4. Allow the test tube and contents to cool.

5. Measure the mass of the test tube and contents.

6. Repeat steps 3 to 5 until the mass of the test tube and contents does not change.

Table 9 shows the results.

Determine the mass of the empty test tube.

Explain why the mass of the test tube and contents decreased.

Suggest why the test tube and contents were heated until the mass did not change.

Energy is taken in from the surroundings when hydrated cobalt chloride is heated.

When 238 g of hydrated cobalt chloride is heated until the mass does not change, 88.1 kJ of energy is taken in. The student heated 2.00 g of hydrated cobalt chloride until the mass did not change.

Calculate the energy taken in during this reaction. Give your answer to 3 significant figures.

What type of reaction takes place when hydrated cobalt chloride is heated?

A student investigated the change in mass when hydrated cobalt chloride was heated. The word equation for the reaction is: hydrated cobalt chloride ⇌ anhydrous cobalt chloride + water

This is the method used.

1. Add 2.0 g of hydrated cobalt chloride to an empty test tube.

2. Measure the mass of the test tube and contents.

3. Heat the test tube and contents gently for 30 seconds.

4. Allow the test tube and contents to cool.

5. Measure the mass of the test tube and contents.

6. Repeat steps 3 to 5 until the mass of the test tube and contents does not change.

Table 1 shows the results.

Determine the mass of the empty test tube.

Explain why the mass of the test tube and contents decreased.

Suggest why the test tube and contents were heated until the mass did not change.

Energy is taken in from the surroundings when hydrated cobalt chloride is heated.

When 238 g of hydrated cobalt chloride is heated until the mass does not change, 88.1 kJ of energy is taken in. The student heated 2.00 g of hydrated cobalt chloride until the mass did not change.

Calculate the energy taken in during this reaction. Give your answer to 3 significant figures.

What type of reaction takes place when hydrated cobalt chloride is heated?

Ammonia is produced in the Haber process. The raw materials for the Haber process are nitrogen and hydrogen. The equation for the reaction is:

Give the sources of the nitrogen and of the hydrogen used in the Haber process.

How does the equation for the reaction show that the atom economy of the forward reaction is 100%?

Figure 4 represents the Haber process.

Explain how the ammonia produced is separated from the unreacted nitrogen and hydrogen in X.

The Haber process uses a temperature of 450 °C and a pressure of 200 atmospheres. Table 6 shows the percentage yield of ammonia produced at 450 °C using different pressures.

Complete Figure 5. The first two points have been plotted. You should:

• use a suitable scale for the x-axis

• plot the remaining data from Table 6

• draw a line of best fit.

Determine the percentage yield of ammonia at 450 °C and 500 atmospheres. Show your working on Figure 5.

The equation for the production of ammonia in the Haber process is:

The forward reaction is exothermic. The conditions used are:

• a temperature of 450 °C

• a pressure of 200 atmospheres

• the presence of an iron catalyst.

Explain why these conditions are chosen for economical production of ammonia in the Haber process. You should include references to the rate of reaction and the position of equilibrium.

This question is about reactions between gases.

When hydrogen gas is heated with iodine gas, hydrogen iodide gas is produced.

The equation for this reversible reaction is:

hydrogen + iodine hydrogen iodide

This reversible reaction reaches equilibrium in a sealed container.

How does the equation show that the reaction is reversible?

Which two statements are correct when the reaction reaches equilibrium?

Tick (✓) two boxes.

The initial mixture of hydrogen and iodine in the sealed container is purple.

Hydrogen iodide is colourless.

How will the colour of the mixture in the sealed container have changed when equilibrium is reached?

Tick (✓) one box.

The rate of reaction between gases is affected by changing the pressure.

Complete the sentences.

When the pressure of the reacting gases is increased,

This is because at higher pressures the distance

Give one other way of changing the rate of reaction between gases.

You should not refer to pressure in your answer.

This question is about organic compounds.

Butane is an alkane with small molecules.

Complete the sentence.

Choose the answer from the box.

Butane can be used as a

Poly(propene) is a polymer.

What is the name of the monomer used to produce poly(propene)?

Tick (✓) one box.

Ethene and steam react to produce ethanol.

The equation for the reversible reaction is:

ethene + steam ethanol

The reaction produces a maximum theoretical mass of 400 kg of ethanol from 243 kg of ethene and 157 kg of steam.

A company produces 380 kg of ethanol from 243 kg of ethene and 157 kg of steam.

The percentage yield of ethanol is less than 100%

Calculate the percentage yield of ethanol.

Use the equation:

What are two possible reasons why the percentage yield of ethanol is less than 100%?

Tick (✓) two boxes.

Ethanol burns in oxygen.

Balance the equation for the reaction.

Two processes for producing ethanol are:

• fermentation

• hydration (reacting ethene with steam).

Table 5 shows information about the processes.

Give two advantages and two disadvantages of using fermentation to produce ethanol.

Advantage of fermentation 1

Advantage of fermentation 2

Disadvantage of fermentation 1

Disadvantage of fermentation 2

This question is about carboxylic acids. Carboxylic acids belong to a homologous series. Table 3 shows information about the first three carboxylic acids in this homologous series.

Complete Table 3.

Ethanoic acid ionises in water. The equation for the reaction is:

Explain how the equation shows that ethanoic acid is a weak acid.

A student adds a solution of ethanoic acid to zinc carbonate in an open flask on a balance. Explain what happens to the mass of the flask and its contents during the reaction.

The student compares the rates of the reaction of zinc carbonate with:

• 0.01 mol/dm³ methanoic acid

• 0.01 mol/dm³ ethanoic acid.

The rate of the reaction with methanoic acid is greater than the rate of the reaction with ethanoic acid. Explain why. You should refer to ions in your answer. Use Table 3.

Ethanoic acid reacts with ethanol to produce an ester.

Give the name of the ester produced when ethanoic acid reacts with ethanol.

Hexanedioic acid and ethanediol join together to produce a polyester. Ethanoic acid and ethanol join together in the same way to produce an ester. Which is the displayed structural formula of the ester produced when ethanoic acid reacts with ethanol? Tick (✓) one box.

This question is about a reversible reaction. The reaction between solutions of iron(III) ions (Fe³⁺) and thiocyanate ions (SCN^–) is reversible. The ionic equation for the reaction is:

Colour of solution: yellow colourless red The colour of the equilibrium mixture is orange at room temperature.

Give the name of the solvent used to dissolve the ions in this reaction.

A few drops of a colourless solution containing a high concentration of thiocyanate ions (SCN –) are added to the orange equilibrium mixture. Explain the colour change observed.

A water bath is set up at a temperature above room temperature. When a test tube containing the orange equilibrium mixture is placed in the water bath, the mixture becomes more yellow. Explain what this shows about the energy change for the forward reaction.

Explain why a change in pressure does not affect the colour of the equilibrium mixture.

Other metal ions form coloured equilibrium mixtures with thiocyanate ions. Which metal ion could form a coloured equilibrium mixture with thiocyanate ions? Tick (✓) one box.

Hydrogen is a raw material in the Haber process.

Hydrogen is produced from methane.

The word equation for the reaction is:

methane + steam carbon monoxide + hydrogen

How can you tell that the reaction is reversible?

The forward reaction is endothermic.

Name the type of energy change in the reverse reaction.

A nickel catalyst is used in this reaction.

Why is a catalyst used in this reaction?

Tick (✓) two boxes.

The Haber process also uses nitrogen to produce ammonia.

Figure 1 shows how the world production of ammonia changed between 1950 and 2010.

Describe how the world production of ammonia changed between 1950 and 2010.

Most of the ammonia produced is used to make fertilisers.

Why did the world production of ammonia change between 1950 and 2010?

Tick (✓) two boxes.

Table 1 shows data about four fertilisers, A, B, C and D.

Which combination of fertilisers A, B, C and D provides all of the elements needed for an NPK fertiliser?

Use Table 1.

Tick (✓) one box.

Which fertiliser is not made using ammonia?

Use Table 1.

Tick (✓) one box.