The effect of changing conditions on equilibrium

This question is about ammonia.

Ammonia is produced from nitrogen and hydrogen in the Haber process.

Hydrogen is produced from methane and steam.

The equation for one of the reactions in the production of hydrogen is:

The forward reaction absorbs energy from the surroundings.

Explain why a high temperature is used in this reaction.

Explain why as low a pressure as possible is used in this reaction.

A nickel catalyst is used in this reaction.

What is the effect of the nickel catalyst on the position of equilibrium?

Tick (✓) one box.

The nitrogen needed in the Haber process is obtained from air.

Calculate the approximate volume of air required to obtain 50 dm³ of nitrogen.

Figure 9 shows how ammonia is produced from nitrogen and hydrogen.

Explain how the mixture of ammonia, nitrogen and hydrogen is separated at X.

Ammonia is used to produce fertilisers.

Nitrogen is released into the air when bacteria break down fertilisers and dead plant matter.

One of the reactions during the production of hydrogen from methane (natural gas) releases carbon dioxide into the air.

The use of nitrogen to produce ammonia is more sustainable than the use of hydrogen to produce ammonia.

Give three reasons why.

This question is about sulfuric acid.

Sulfuric acid contains sulfate ions.

Describe the test for the presence of sulfate ions in sulfuric acid.

Give the result of the test.

One stage in the industrial production of sulfuric acid is the reaction of sulfur dioxide with oxygen to produce sulfur trioxide.

This reversible reaction reaches dynamic equilibrium.

Figure 7 shows the percentage yield of sulfur trioxide in this reaction at different temperatures.

Which statement about the forward reaction is correct?

Use Figure 7.

Tick (✓) one box.

The equation for the reaction is:

Explain why the percentage yield of sulfur trioxide in this reaction is greater if the pressure is higher.

In industry, the reaction is done at 450 °C and atmospheric pressure.

Under these conditions the yield of sulfur trioxide is 86%.

Suggest two reasons why a higher pressure is not used.

This reaction uses a catalyst to increase the rate of the reaction.

The catalyst is a metal oxide.

Which is the most likely metal in the metal oxide catalyst?

Use the periodic table.

Tick (✓) one box.

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.

This question is about alkenes and alcohols. Ethene is an alkene produced from large hydrocarbon molecules. Large hydrocarbon molecules are obtained from crude oil by fractional distillation.

Name the process used to produce ethene from large hydrocarbon molecules.

Describe the conditions used to produce ethene from large hydrocarbon molecules.

Ethanol can be produced from ethene and steam. The equation for the reaction is:

The forward reaction is exothermic.

Explain how the conditions for this reaction should be chosen to produce ethanol as economically as possible.

Ethanol can also be produced from sugar solution by adding yeast. Name this process.

Butanol can be produced from sugar solution by adding bacteria. Sugar solution is broken down in similar ways by bacteria and by yeast. Suggest the reaction conditions needed to produce butanol from sugar solution by adding bacteria.

Ethanol and butanol can be used as fuels for cars.

A car needs an average of 1.95 kJ of energy to travel 1 m Ethanol has an energy content of 1300 kilojoules per mole (kJ/mol). Calculate the number of moles of ethanol needed by the car to travel 200 km

When butanol is burned in a car engine, complete combustion takes place. Write a balanced equation for the complete combustion of butanol. You do not need to include state symbols.

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.

This question is about reversible reactions and equilibrium.

Hydrogen is used to produce ammonia in the Haber process.

The hydrogen is made in two stages.

Stage 1 is the reaction of methane and steam to produce carbon monoxide and hydrogen.

The equation for the reaction is:

Calculate the atom economy for the formation of hydrogen in stage 1.

Relative atomic masses (A_r): H = 1 C = 12 O = 16

Explain why a low pressure is used in stage 1.

Give your answer in terms of equilibrium.

Stage 2 uses the carbon monoxide produced in stage 1.

The carbon monoxide is reacted with more steam to produce carbon dioxide and more hydrogen.

The equation for the reaction in stage 2 is:

What is the effect of increasing the pressure on the equilibrium yield of hydrogen in stage 2 ?

Figure 10 shows the percentage yield of ammonia produced at different temperatures and pressures in the Haber process.

A temperature of 450 °C and a pressure of 200 atmospheres are used in the Haber process.

A student suggested that a temperature of 350 °C and a pressure of 285 atmospheres could be used instead of those used in the Haber process.

Determine how many times greater the percentage yield of ammonia obtained would be.

Use Figure 10.

A pressure of 285 atmospheres is not used in the Haber process instead of 200 atmospheres.

Give one reason why.

How does Figure 10 show that the forward reaction in the Haber process is exothermic?

World production of ammonia is now about 30 times greater than it was in 1950.

Suggest why the demand for ammonia has increased.

This question is about methanol.

Methanol is broken down in the body during digestion. What type of substance acts as a catalyst in this process?

Tick one box.

In industry, methanol is produced by reacting carbon monoxide with hydrogen. The equation for the reaction is:

How many moles of carbon monoxide react completely with 4.0 10³ moles of hydrogen?

Tick one box.

The reaction is carried out at a temperature of 250 ºC and a pressure of 100 atmospheres. The forward reaction is exothermic. Explain what happens to the yield of methanol if a temperature higher than 250 ºC is used.

A pressure of 100 atmospheres is used instead of atmospheric pressure. The higher pressure gives a greater yield of methanol and an increased rate of reaction. Explain why.

A catalyst is used in the reaction to produce methanol from carbon monoxide and hydrogen.

Explain how a catalyst increases the rate of a reaction.

Suggest why a catalyst is used in this industrial process. Do not give answers in terms of increasing the rate of reaction.

Suggest the effect of using the catalyst on the equilibrium yield of methanol.