The effect of changing conditions on equilibrium

This question is about ammonia.

Ammonia is a gas.

Suggest why the litmus paper used to test for ammonia gas has to be damp.

Ammonia can be made on an industrial scale using the Haber process.

The equation for the reaction is

The reaction can reach a dynamic equilibrium.

Explain what happens when the reaction reaches dynamic equilibrium

Figure 8 shows the changes in percentage yield of ammonia at equilibrium as temperature increases, at a pressure of 300 atmospheres and at a pressure of 1000 atmospheres.

Which row of the table will give the highest percentage yield of ammonia at equilibrium?

In industry, a pressure of 200 atmospheres is used for the Haber process.

Using Figure 8, explain what happens to the position of dynamic equilibrium if the process is carried out at 100 atmospheres.

Ammonia can also be made by heating ammonium chloride.

A sample of solid ammonium chloride is heated in a boiling tube.

After a few minutes ammonium chloride, a white solid, is also seen at the top of the boiling tube, as shown in Figure 9.

Explain how ammonium chloride is formed at the top of the boiling tube.

Hydrogen can be produced by the reaction of methane with steam.

Methane reacts with steam in the presence of a nickel catalyst to produce hydrogen and a dynamic equilibrium is reached.

The equation for this equilibrium reaction is

methane

The forward reaction takes in heat energy and is endothermic.

Describe the effect of the catalyst on the rate of attainment of equilibrium and on the equilibrium yield of products.

*(ii) A manufacturer produces hydrogen by the reaction of methane with steam in the presence of a nickel catalyst using the conditions

pressure 20 atmospheres

Explain what effect there would be on the rate of attainment of equilibrium and the equilibrium yield of hydrogen if the manufacturer were to use a higher temperature of 1000C at a lower pressure of 10 atmospheres without changing the catalyst.

Using the equation for the reaction

calculate the maximum volume of products, in dm³, that could be formed by the complete reaction of 650 dm³ of methane.

(assume all volumes of gases are measured under the same conditions of temperature and pressure)

maximum volume of products =_........

Using the same equation for the reaction

calculate the maximum mass, in g, of carbon dioxide for every 1800 dm³ of hydrogen, measured at room temperature and pressure, produced in this reaction.

(relative formula mass: CO₂ = 44; 1 mol of any gas at room temperature and pressure occupies 24 dm³)

mass of carbon dioxide =_........

Ammonia is manufactured in the Haber process by the reversible reaction between nitrogen and hydrogen.

Write the balanced equation for the reversible reaction between nitrogen and hydrogen to make ammonia, NH₃.

Which row shows the typical conditions of temperature and pressure used in the Haber process?

In the Haber process, iron is added to the vessel where the nitrogen and hydrogen react.

State the purpose of the iron.

The reaction between nitrogen and hydrogen to make ammonia can reach dynamic equilibrium.

The reaction gives out heat.

Explain how the position of equilibrium changes if the temperature is decreased.

Compound A is a dark brown gas.

Compound B is a colourless gas.

Two molecules of A combine to form one molecule of B in a reversible reaction.

You are given

• a sealed glass tube containing an equilibrium mixture of A and B

• a beaker

• a kettle

• some ice

At room temperature, the equilibrium mixture is a pale brown colour.

Devise an experiment to show how the position of equilibrium of this reaction is affected by temperature.

The sealed tube must not be opened.

When hydrogen is removed from an alkane, an alkene is formed.

This is an example of a dehydrogenation reaction.

Under certain conditions the dehydrogenation of propane forms propene and a dynamic equilibrium is reached.

State what is meant by dynamic in this context.

*(ii) The equation for this equilibrium reaction is

propane propene

The forward reaction takes in heat energy and is endothermic. A manufacturer produces large quantities of propene using this equilibrium reaction.

Suggest, with explanations, suitable conditions that the manufacturer could use to maximise the yield and rate of production of propene from propane.

C₃H₈(g) C₃H₆(g) + H₂(g) propane propene

State the maximum volume of propene, in dm³, formed by the dehydrogenation of 300 dm³ of propane.

(assume all volumes of gases are measured under the same conditions of temperature and pressure)

maximum volume of propene =_........

900 dm³ of propane, measured at room temperature and pressure, were dehydrogenated to form propene.

propane propene

Calculate the maximum mass, in kg, of hydrogen formed in this reaction.

(relative atomic mass: H = 1.0; 1 mol of any gas at room temperature and pressure occupies 24 dm³)

mass of hydrogen =_........

Copper carbonate reacts with dilute nitric acid.

During the reaction the copper carbonate powder completely disappears.

State what can be deduced about the amount of acid used.

During the reaction, the pH of the mixture changed from 2 to 6.

By what factor has the concentration of the hydrogen ions in the mixture changed?

Using different reactants, a solution of copper sulfate was prepared.

Describe what should be done to obtain copper sulfate crystals from this copper sulfate solution.

When chloride ions are added to a pale blue solution containing copper ions, the mixture turns yellow.

This is a reversible reaction.

pale blue solution + chloride ions yellow solution + water

What effect does the removal of chloride ions have on the colour of the yellow mixture?

Hydrated copper sulfate has the formula CuSO₄.5H₂O. The formula tells us that each mole of copper sulfate contains 5 moles of water.

A sample of CuSO₄.5H₂O was heated gently until all the water was removed to form anhydrous copper sulfate, CuSO₄.

The mass of water formed was 4.5 g.

Calculate the mass of hydrated copper sulfate that was heated.

(relative atomic masses: H = 1.0, O = 16.0; relative formula mass: CuSO₄.5H₂O = 249.5)

mass of CuSO₄.5H₂O =_........

Hydrogen-oxygen fuel cells, rather than chemical cells, can be used to power some vehicles.

Give one advantage of using a hydrogen-oxygen fuel cell, rather than using a chemical cell, to power a vehicle.

Complete the half-equation for the reaction taking place at one of the electrodes in a hydrogen-oxygen fuel cell.

Calculate the volume of 48 g of oxygen at room temperature and pressure.

(relative atomic mass: O = 16, 1 mol of gas occupies 24 dm³ at room temperature and pressure)

volume of oxygen =_........

*(d) The hydrogen used in a hydrogen-oxygen fuel cell can be produced from methanol, CH₃OH.

In this reaction the forward reaction is endothermic and heat energy is taken in from the surroundings. The conditions used for this reaction are

• a nickel catalyst

• a temperature of 220 °C

Explain, in terms of their effects on the rate of attainment of equilibrium and the equilibrium yield of hydrogen, why the reaction is carried out using a catalyst at 220 °C rather than without a catalyst at a lower temperature.

Methane reacts with steam to form hydrogen and carbon dioxide.

The reaction takes place in two stages.

Stage 1 takes in heat energy, it is endothermic.

Explain the effect of increasing the temperature on the yield of the products of stage 1.

The overall equation for the process is

0.40 g of methane were fully reacted with steam to form carbon dioxide and hydrogen.

Calculate the maximum volume of hydrogen in dm³, measured at room temperature and pressure, that could be made in this reaction.

(relative formula mass: CH₄ = 16, 1 mol of any gas at room temperature and pressure occupies 24 dm³)

*(b) Hydrogen-oxygen fuel cells can be used to provide electrical energy in a spacecraft.

The reaction that takes place in the fuel cell is

hydrogen + oxygenwater

Evaluate the advantages and disadvantages of providing electrical energy in a spacecraft using hydrogen-oxygen fuel cells rather than chemical cells.

Ammonia is manufactured by the Haber process.

The equation for the reaction is

The reaction is reversible and can reach equilibrium.

An iron catalyst can be used in the reaction.

Which row of the table shows how adding the iron catalyst affects the rate of attainment of equilibrium and the equilibrium yield of ammonia?

Which of the following statements is correct when the reaction reaches equilibrium?

The reaction is carried out at a pressure of 200 atmospheres.

Explain what effect a pressure higher than 200 atmospheres would have on the rate of attainment of equilibrium and on the equilibrium yield of ammonia.

Ammonium sulfate and ammonium nitrate are used as fertilisers as they both contain nitrogen, which will increase the yield of crops.

Suggest one other reason for using solid ammonium sulfate and solid ammonium nitrate as nitrogenous fertilisers.

Ammonium nitrate can be made by the reaction of ammonia with nitric acid.

Write the balanced equation for this reaction.

(a) Nitric acid can be titrated with a solution of ammonia.

State the type of reaction occurring when nitric acid reacts with ammonia.

What salt is formed in this reaction?

In one stage of the production of nitric acid, nitrogen oxide, NO, is reacted with oxygen to make nitrogen dioxide, NO₂.

Calculate the minimum volume of air, measured at room temperature and pressure, required to react with 1000 g nitrogen oxide to form nitrogen dioxide.

Assume that the air contains 20% oxygen by volume. (relative atomic masses: N = 14, O = 16 1 mol of gas occupies 24 dm³ at room temperature and pressure)

*(c) In another stage in the production of nitric acid, ammonia is reacted with oxygen to form nitrogen oxide and water.

Heat energy is given out when ammonia reacts with oxygen.

The conditions chosen for the reaction are

• excess air, rather than just the right amount

• a pressure of 10 atm, rather than atmospheric pressure

• a temperature of 900 °C, rather than room temperature.

Explain the effect of the conditions chosen on the equilibrium yield of nitrogen oxide and on the rate of attainment of equilibrium.