Dynamic 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.

When ethanoic acid reacts with ethanol in the presence of concentrated sulfuric acid, one of the products is ester A.

This is the equation for the reaction.

ethanoic acid
ethanol
water

Draw a circle around the functional group in ethanoic acid.

Give the displayed formula of ester A.

Name ester A.

The reaction mixture is kept in a sealed container until dynamic equilibrium is reached.

State what is meant by the term dynamic equilibrium.

During the reaction, the number of moles of ethanoic acid in the reaction mixture decreases, but the number of moles of concentrated sulfuric acid does not change.

Give a reason why the number of moles of concentrated sulfuric acid does not change.

A student does a titration to find the accurate volume of sodium hydroxide solution needed for complete neutralisation.

The student starts by using a pipette to transfer 25.0 cm³ of the reaction mixture to a conical flask.

Describe how the student should complete the titration.

An organic compound has this percentage composition by mass.

C = 40 % H = 6.7 % O = 53.3 %

Show that the empirical formula of the compound is CH₂O

Draw the structural formula of a compound with the molecular formula C₂H₄O₂

Methanoic acid (HCOOH) reacts with sodium carbonate solution to give three products.

Complete the equation for this reaction.

2HCOOH + Na₂CO_{3 ........} +_........ +_........

State what you would observe in this reaction.

Methanoic acid also reacts with propanol to form an ester.

The equation for the reaction is

Give the name of the ester that forms.

State what is meant by the symbol.

When this reaction occurs in a sealed container, the reaction can reach dynamic equilibrium.

Give one characteristic of a reaction at dynamic equilibrium.

A polyester forms when butanedioic acid reacts with ethanediol.

The diagram shows the repeat unit of the polyester that forms.

O O

Give the name of this type of polymerisation.

Draw the structural formulae of the two monomers used to make this polyester.

This question is about esters.

Ester A reacts with water to form ethanoic acid and ethanol.

The displayed formulae of the reactants and products are shown in this equation

ester A

The molar enthalpy change (Δ H) for the reaction is 0 kJ/mol.

Draw a ring around the functional group in ester A.

Give the name of ester A.

Describe a chemical test, other than using an indicator, to show that the reaction mixture contains ethanoic acid.

Explain why the molar enthalpy change (Δ H) for the reaction between ester A and water is 0 kJ/mol.

In your answer, refer to the bonds broken and the bonds formed.

A mixture of ester A and water is left in a sealed container until the reaction mixture reaches dynamic equilibrium.

Describe what is meant by dynamic equilibrium.

Explain why adding a catalyst does not change the position of equilibrium.

The ethanoic acid produced in the reaction is completely neutralised by 22.75 cm³ of 0.150 mol/dm³ barium hydroxide solution.

The equation for the neutralisation reaction is

Calculate the amount, in moles, of ethanoic acid neutralised.

Give your answer to 3 significant figures.

The structures of two organic compounds are shown.

These compounds react together to form a polymer.

Give the repeat unit of the polymer formed.

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)

Ethanol, C₂H₅OH, can be oxidised to produce ethanoic acid, CH₃COOH, by heating it with potassium dichromate(VI).

Name one other reactant needed for this reaction to occur.

Which colour change occurs during this reaction?

When ethanol is burned in air, complete combustion can occur.

The equation for this reaction is

This equation can also be written using displayed formulae to show all the covalent bonds in the molecules.

H H

H H

The table gives the bond energies for these bonds.

Use values from the table to calculate the energy needed to break all the bonds in the reactants.

energy needed_........

Use values from the table to calculate the energy released when all the bonds in the products are formed.

energy released_........

Calculate the molar enthalpy change (Δ H) in kJ/mol, for the complete combustion of ethanol.

Include a sign in your answer.

ΔH =_........ kJ/mol

Ethanol reacts with methanoic acid, HCOOH, in the presence of an acid catalyst to form an ester.

The equation for the reaction is

Give the name of the ester that forms.

Draw the displayed formula for this ester.

When this reaction takes place in a sealed container, the reaction can reach dynamic equilibrium.

Give two characteristics of a reaction at dynamic equilibrium.

Methanoic acid reacts with sodium carbonate to form sodium methanoate, carbon dioxide and water.

The equation for the reaction is

Calculate the volume, in cm³, of carbon dioxide gas produced when 2.3 g of methanoic acid reacts completely with sodium carbonate.

[M_r of HCOOH = 46]

[molar volume of carbon dioxide at rtp = 24 dm³]

(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.