The effect of changing conditions on equilibrium

Gaseous ethanol is manufactured by reacting ethene gas with steam.

This is the equation for the reaction.

The pressure on an equilibrium mixture of the three gases is decreased. All the other conditions are kept the same.

Predict the effect of this change on the yield of ethanol at equilibrium, giving a reason for your answer.

Predict the effect of adding a catalyst on the yield of ethanol at equilibrium, giving a reason for your answer.

The equation shows the displayed formulae for the reactants and products.

The table gives the bond energies.

Using the data in the table and the equation, show that the enthalpy change, Δ H, is approximately –40 kJ / mol.

Explain, in terms of bonds broken and bonds made, why this reaction is exothermic.

Draw an energy level diagram for the reaction between ethene and steam.

Label the enthalpy change, Δ H.

Ethanoic acid reacts with ethanol to form ester A and water.

Complete the equation by adding the displayed formula of ester A.

ester A

Give the name of ester A.

Methane reacts with steam to form carbon monoxide and hydrogen.

This is the equation for the reaction.

State why carbon monoxide is poisonous to humans.

Explain the effect, if any, on the yield of hydrogen at equilibrium when a nickel catalyst is used.

The reaction conditions for this reaction are a temperature of 700 °C and a pressure of 5 atmospheres.

The temperature of the reaction mixture is reduced to 600 °C, but the pressure is kept at 5 atmospheres.

Explain the effect on the yield of hydrogen at equilibrium.

The pressure of the reaction mixture is reduced to 4 atmospheres, but the temperature is kept at 700 °C.

Explain the effect on the yield of hydrogen at equilibrium.

Calculate the volume, in dm³, of methane gas at rtp needed to produce 6.6 tonnes of hydrogen gas.

[at rtp, molar volume = 24 dm³ 1 tonne = 10⁶g]

Give your answer in standard form.

Methanol is made by the reaction between hydrogen and carbon monoxide.

This is the equation for the reaction.

A mixture of hydrogen and carbon monoxide is left until dynamic equilibrium is reached.

Give two characteristics of a reaction at dynamic equilibrium.

Give a reason why adding a catalyst does not affect the yield of methanol.

The temperature of the reaction mixture is decreased at constant pressure.

Explain the effect of this change on the yield of methanol.

The pressure of the reaction mixture is increased at constant temperature.

Explain the effect of this change on the yield of methanol.

Show that the molar enthalpy change, Δ H, for the reaction is −119 kJ / mol.

Explain why this reaction is exothermic.

The diagram shows the displayed formula of an ester that is made from methanol and a carboxylic acid.

H H

H H

Draw a circle around the functional group of the ester.

Give the displayed formula of the carboxylic acid used to make this ester.

In the presence of an iron catalyst, nitrogen reacts with hydrogen to form ammonia.

The reaction conditions used are a temperature of 450C and a pressure of 200 atmospheres.

This is the equation for the reaction.

State what the symbol represents.

Give the reason for using a catalyst.

The reaction mixture is kept at a pressure of 200 atmospheres, but the

Explain the effect of this change on the yield of ammonia at equilibrium.

The reaction mixture is kept at a temperature of 450C, but the pressure is increased to 300 atmospheres.

Explain the effect of this change on the yield of ammonia at equilibrium.

Draw an energy level diagram for the reaction between nitrogen and hydrogen.

Include the reactants, products and Δ H in your diagram.

QUESTION 7 CONTINUES ON NEXT PAGE

At the start of the reaction, 48 dm³ of nitrogen is added to 120 dm³ of hydrogen at rtp.

[molar volume of any gas at rtp = 24 dm³]

Show by calculation that the nitrogen is in excess.

The yield of ammonia at equilibrium is 20 %.

Calculate the volume, in dm³, of ammonia formed from 120 dm³ of hydrogen.

This question is about three stages in the manufacture of sulfuric acid.

In stage 1, sulfur is burned in oxygen to form sulfur dioxide gas.

State one environmental problem caused by the release of sulfur dioxide into the atmosphere.

A mass of 6.4 tonnes of sulfur is burned to produce sulfur dioxide gas.

Calculate the maximum volume, in dm³, of sulfur dioxide gas that can be produced at rtp.

[molar volume of sulfur dioxide gas at rtp = 24 dm³]

[1 tonne = 10⁶g]

Give your answer in standard form.

In stage 2, sulfur dioxide is reacted with oxygen to form sulfur trioxide gas.

The yield of sulfur trioxide is approximately 98%.

A catalyst is used in this reaction.

Explain how a catalyst increases the rate of a reaction.

The temperature is kept constant.

Give a reason why increasing the pressure would increase the yield of sulfur trioxide.

Suggest why it is not necessary to increase the pressure in stage 2.

In stage 3, the sulfur trioxide is reacted with concentrated sulfuric acid to form a liquid called oleum, H₂S₂O₇

The oleum is then added to water to form concentrated sulfuric acid.

Complete the chemical equations for these two reactions.

Sulfuric acid reacts with ammonia to form ammonium sulfate, (NH₄)₂SO₄

Calculate the percentage by mass of nitrogen in ammonium sulfate.

[M_r of (NH₄)₂SO₄ = 132]

Hydrogen gas and iodine gas react together to form hydrogen iodide gas.

The pressure of an equilibrium mixture of the three gases is increased.

Predict the effect of this change on the yield of hydrogen iodide at equilibrium, giving a reason for your answer.

A catalyst is added to an equilibrium mixture of the three gases.

Predict the effect of the catalyst on the yield of hydrogen iodide at equilibrium, giving a reason for your answer.

Hydrogen gas reacts with fluorine gas to form hydrogen fluoride gas.

The table gives some bond energies.

Use the equation and the data in the table to calculate the enthalpy change (Δ H) in kJ/mol, for the reaction.

Include a sign in your answer.

ΔH =_........ kJ/mol

Draw an energy level diagram for the reaction between hydrogen and fluorine.

Label the enthalpy change, Δ H.

This question is about ammonia gas, NH₃

Ammonia can be prepared in a laboratory from the reaction between ammonium chloride, NH₄Cl, and sodium hydroxide. The other products of the reaction are sodium chloride and water.

Give a chemical equation for this reaction.

Give a test for ammonia gas.

In industry, ammonia is produced from nitrogen and hydrogen.

The equation for this reaction is

In a sealed container, the reaction can reach a position of dynamic equilibrium.

Explain the meaning of the term dynamic equilibrium.

The graph shows the percentage yield of ammonia at equilibrium for different temperatures and pressures.

Using the graph, explain if the forward reaction is exothermic or endothermic.

(TOTAL FOR PAPER = 70 MARKS)

This question is about reactions involving gases.

Potassium carbonate reacts with dilute hydrochloric acid to produce carbon dioxide gas.

The equation for the reaction is

Calculate the volume, in cm³, of carbon dioxide gas produced when 6.9 g of potassium carbonate reacts with excess dilute hydrochloric acid.

[M_r of K₂CO₃ = 138]

[molar volume of CO₂ at rtp = 24 dm³]

This reaction involving gases is in dynamic equilibrium at a temperature of 225C.

Predict the effect on the yield of CO(g) at equilibrium when the temperature is increased without changing the pressure.

Give a reason for your answer.

Predict the effect on the yield of CO(g) at equilibrium when the pressure is increased without changing the temperature.

Give a reason for your answer.

(a) Ethanol, C₂H₅OH, can be produced by the fermentation of glucose, C₆H₁₂O₆

Complete the equation for the fermentation of glucose.

State why it is necessary for fermentation to be done in the absence of air.

Explain why the temperature should not be higher than 40 °C.

When 4 mol of glucose is fermented, a mass of 55.2 g of ethanol is produced.

Show that the percentage yield of ethanol is 15%.

[M_r of C₂H₅OH = 46]

Ethanol can also be produced by the reaction between ethene and steam.

The equation for the reaction is

This reaction is in dynamic equilibrium.

Give two features of a reaction in dynamic equilibrium.

When the equilibrium mixture is heated, the yield of ethanol decreases.

Explain whether the forward reaction is exothermic or endothermic.

Carboxylic acids react with alcohols to form esters.

The displayed formula of an ester is

H H O

H H H H

Carboxylic acid A and alcohol B react to produce this ester.

Give the displayed formula of carboxylic acid A and of alcohol B.

Indicators can be used to test for carboxylic acids.

Describe a different chemical test for a carboxylic acid.

Dinitrogen tetraoxide, N₂O₄, is a colourless gas.

Nitrogen dioxide, NO₂, is a brown gas.

The two gases can exist together in dynamic equilibrium according to the equation

Explain what is meant by the term dynamic equilibrium.

Some N₂O₄ and some NO₂ are put into a sealed gas syringe and allowed to form an equilibrium mixture.

This equilibrium mixture is brown.

The pressure of the gas in the syringe is increased by pushing in the piston. The mixture is then allowed to reach a new equilibrium at the same temperature as before.

Explain why the new equilibrium mixture contains less NO₂ than the original equilibrium mixture.

A student suggests that the new equilibrium mixture would be lighter in colour than the original equilibrium mixture, as there is now less NO₂ present.

Suggest why the new equilibrium mixture is actually darker than the original.

Carbon monoxide, CO, and oxides of nitrogen are produced in a car engine when petrol is burned.

These oxides can be partly removed by using a catalytic converter fitted to the car’s exhaust system.

State how oxides of nitrogen are produced in the car engine.

Give a disadvantage of allowing oxides of nitrogen to escape into the atmosphere.

Write a chemical equation for the reaction between nitrogen monoxide, NO, and carbon monoxide to form carbon dioxide and nitrogen.

Hydrogen gas can be produced by reacting a mixture of methane and steam in the presence of a nickel catalyst.

The reaction conditions are a temperature of 700C and a pressure of 5 atmospheres.

The equation for the reaction is

What does the symbol represent?

The mixture of methane and steam is heated to a temperature greater than 700 °C but the pressure is kept at 5 atmospheres.

Predict the effect of this change on the yield of hydrogen at equilibrium, giving a reason for your answer.

The mixture of methane and steam is kept at the same temperature of 700 °C but the pressure is increased to more than 5 atmospheres.

Predict the effect of this change on the yield of hydrogen at equilibrium, giving a reason for your answer.

Calculate the volume, in dm³, of hydrogen gas at rtp that is produced when 10 tonnes of methane gas completely react with steam.

[molar volume of hydrogen at rtp is 24 dm³]

Give your answer in standard form.