Reversible reactions

Screenwash is a mixture designed to keep car windscreens clean.

The components in screenwash include glycerol, methanol and water.

Screenwash is made by mixing the components in carefully measured quantities so that the product has the required properties.

What name is given to this type of mixture?

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Glycerol has the formula C₃H₈O₃

How many atoms are there in one molecule of glycerol?

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Incomplete combustion happens when glycerol burns in limited oxygen.

Incomplete combustion produces carbon monoxide gas.

Why can the production of carbon monoxide gas be a problem?

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Complete combustion happens when methanol (CH₄O) burns in excess oxygen.

Balance the equation for the reaction.

Methanol can be produced by the reaction of carbon dioxide with hydrogen.

Describe the test for hydrogen gas.

Give the result of the test.

Carbon dioxide is a greenhouse gas.

An increase in greenhouse gases in the atmosphere has led to an increase in average global temperature.

The increase in average global temperature has caused global climate change.

Give two effects of global climate change.

Anhydrous cobalt chloride can be used to test for water.

The word equation for the reaction is:

anhydrous cobalt chloride + water hydrated cobalt chloride (blue) (pink)

Suggest one observation that could be made when water is added to anhydrous cobalt chloride.

The reaction between anhydrous cobalt chloride and water is exothermic.

What type of reaction is the reverse reaction?

This question is about methanol.

Methanol is used in screenwash.

Screenwash is used to keep car windscreens clean.

Screenwash is a formulation.

Define the term ‘formulation’.

Carbon monoxide and hydrogen are used to produce methanol.

The conditions used in the production of methanol are:

• high temperature

• high pressure

• a catalyst.

The equation for the reaction is:

91 kJ/mol of energy is transferred during the exothermic forward reaction.

How much energy is transferred when methanol is decomposed into carbon monoxide and hydrogen?

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A scientist developed a principle to predict the effect of changing conditions on a system at equilibrium.

What was the name of the scientist?

What is the effect of increasing the temperature on the proportion of methanol in the equilibrium mixture?

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What is the effect of using a catalyst on the proportion of methanol in the equilibrium mixture?

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Explain the effect of increasing the pressure on the proportion of methanol in the equilibrium mixture.

Explain the effect of using a catalyst on the rate of production of methanol.

The catalyst allows the reaction to take place at a lower temperature.

Explain one advantage of using a lower temperature in the production of methanol.

Do not refer to the position of equilibrium in your answer.

Methanol (CH₃OH) can also be produced by reacting carbon dioxide with hydrogen.

Water is the other product of the reaction.

Write a balanced equation for the reaction.

Different tests can be used to identify chemicals.

A student measured the melting points of four substances.

Table 1 shows the results.

Which substance was pure?

Give one reason for your answer.

Anhydrous copper sulfate can be used to test for water.

The word equation for the reaction is:

anhydrous copper sulfate + water hydrated copper sulfate

Complete the sentence.

Choose answers from the box.

When water is added to anhydrous copper sulfate, the colour changes

The reaction between anhydrous copper sulfate and water is reversible.

How does the word equation show that the reaction is reversible?

The formula of anhydrous copper sulfate is CuSO₄

What is the total number of atoms in the formula CuSO₄?

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Chlorine is a gas.

Describe the test for chlorine.

Give the result.

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?

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The concentration of oxygen is increased.

What is the effect on the position of the equilibrium?

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The pressure is decreased.

What is the effect on the position of the equilibrium?

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The temperature is increased.

What is the effect on the position of the equilibrium?

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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.

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?

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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?

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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?

Fresh water contains low levels of dissolved salts.

Water reacts with anhydrous copper sulfate in a reversible reaction.

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

How does the equation show that the reaction is reversible?

Complete the sentences. Choose answers from the box.

Figure 1 shows anhydrous copper sulfate in a sealed container.

Suggest one reason why anhydrous copper sulfate is kept in a sealed container.

Sodium chloride dissolves in water to form sodium chloride solution.

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

Name the process used to obtain solid sodium chloride from sodium chloride solution.

Two processes used to obtain potable water from fresh water are:

• filtering

• sterilising.

Give one reason why each process is used.

Which type of water is the easiest to obtain potable water from? Tick (✓) one box.

Which of the following is the first stage of waste water treatment? Tick (✓) one box.

The methods used to produce potable water depend upon available sources of water.

Suggest how copper sulfate can be used as a test for the presence of water.

The boiling point is used to check the purity of a sample of water.

In chemistry, what is meant by a ‘pure substance’?

The boiling point of a 250 g sample of water was 100.60 °C.

The boiling point of pure water in a data book is 100.00 °C.

Each 1% of impurity increases the boiling point of water by 0.12 °C.

Calculate the mass of the impurity in the sample of water.

Explain how distillation is used to obtain potable water from salty water.

Obtaining potable water from salty water is more expensive than obtaining potable water from ground water.

Explain why.

Refer to the processes used in both methods in your answer.

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?

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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?

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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.