Bond energy calculations

This question is about ethanol, C₂H₅OH, which can be used as a fuel.

Ethanol can be produced by the fermentation of glucose solution.

Name the substance that is added that causes the fermentation of glucose solution.

Which temperature is most suitable for fermentation?

Explain why fermentation is done in the absence of air.

This is the equation for the combustion of ethanol.

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

The table shows some bond energies.

Use the bond energies to show that the molar enthalpy change, Δ H, is about −1300 kJ / mol.

Complete the energy level diagram for the reaction between C₂H₅OH and O₂

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

Ethanol reacts with compound A to produce ester B and compound C.

This is the equation for the reaction.

H H
H O

ester B

Draw the displayed formula for compound A and for compound C.

Name ester B.

This question is about crude oil.

Describe how crude oil is separated into fractions by fractional distillation.

Some of the long-chain alkanes obtained from fractional distillation are cracked, producing shorter-chain alkanes and ethene.

Give the conditions necessary for cracking to occur.

Explain why shorter-chain alkanes are more useful than longer-chain alkanes.

Ethene reacts with bromine.

The equation shows the displayed formulae of the reactants and product.

H H

Br Br

The table shows some bond energies.

Show that the molar enthalpy change, Δ H, for this reaction is about –100 kJ/mol.

ΔH =_........ kJ/mol

Explain why the reaction between ethene and bromine is exothermic.

Refer to bond energies in your answer.

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.

This question is about hydrogen chloride (HC l).

Hydrogen chloride is a covalent compound.

State, in terms of electrostatic attraction, what is meant by a covalent bond.

When hydrogen chloride gas is dissolved in an organic solvent, the hydrogen chloride remains a covalent molecule.

When hydrogen chloride gas is dissolved in water, ions are formed.

Explain what happens when dry blue litmus paper is dipped into separate samples of each solution.

In the presence of ultraviolet radiation, hydrogen reacts with chlorine to form hydrogen chloride.

This is the equation for the reaction.

The table shows the bond energies.

Calculate the enthalpy change (Δ H), in kJ/mol, for the reaction.

Include a sign in your answer.

ΔH =_........ kJ/mol

Draw a reaction profile for the reaction.

Label the reactants, the products, ΔH and the activation energy (E_a).

Sodium chloride is an ionic compound.

Explain why sodium chloride conducts electricity when it is molten or in solution, but not when it is solid.

A solution of sodium chloride can be electrolysed using this apparatus.

If the solution is dilute, a significant amount of oxygen collects at P.

Complete the ionic half-equation for this reaction.

If the solution is concentrated, chlorine is the main product that collects at P.

This is the ionic half-equation for the reaction.

State why this is an oxidation reaction.

The gas that collects at Q is hydrogen.

Give a test for hydrogen.

Explain how hydrogen gas forms at the negative electrode.

Hydrogen reacts with oxygen to form water.

The equation shows the covalent bonds in the molecules.

The table gives the bond energies.

Use the equation and the values in the table to calculate the enthalpy change, Δ H, for the reaction.

Include a sign in your answer.

Complete the diagram to show the energy levels of the reactants and products, and the enthalpy change, Δ H.

Ethanoic acid reacts with methanol to form an ester.

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

H H H H

Give the name of a suitable catalyst to increase the rate of this reaction.

State how you would know that an ester has formed.

Give the name of this ester.

The table shows the number of bonds in the reactants and the number of bonds in the products.

State which two bonds need to be broken in the reactants.

Explain why the enthalpy change in this reaction is approximately 0 kJ / mol.

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.

This question is about hydrazine, N₂H₄

This is the displayed formula for a molecule of hydrazine.

Complete the dot‑and‑cross diagram for hydrazine.

Use the data in the table to calculate the total energy needed to break all the bonds in the reactants.

Use the data in the table to calculate the total energy released when all the bonds in the products are made.

Calculate the enthalpy change, Δ H, in kJ/mol, for the reaction.

ΔH =_........ kJ/mol

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

A sample of hydrazine is completely decomposed.

This is the equation for the decomposition of hydrazine.

The products of the decomposition are bubbled through 1100 cm³ of water.

The ammonia completely dissolves in the water, but nitrogen is insoluble in water.

The nitrogen has a volume of 1570 cm³ at room temperature and pressure (rtp).

Calculate the concentration, in mol/dm³, of the ammonia solution.

Give your answer to 3 significant figures.

[for a gas at rtp, molar volume = 24 000 cm³]

concentration =_........ mol/dm

This question is about reactions involving nitrogen.

In a car engine, nitrogen reacts with oxygen to form nitrogen monoxide.

The equation for the reaction is

Draw a labelled reaction profile diagram showing Δ H and the activation energy for the reaction.

Energy

Calculate the total amount of energy, in kJ, needed to break the bonds in the reactants.

Calculate the total amount of energy, in kJ, released in forming the bonds in the product.

Calculate the enthalpy change, Δ H, for the reaction.

You should include a sign in your answer.

A student uses this apparatus to find the heat energy supplied by a liquid fuel.

The student burns some fuel to heat the water in the copper container and measures the change in temperature.

The student notices that the bottom of the container turns black.

Give the name of the black substance that forms on the bottom of the container.

In one experiment, the student burns 0.92 g of ethanol.

The student calculates that the heat energy absorbed by the water is 18.2 kJ.

Show that the results of this experiment give an approximate value for the enthalpy of combustion of ethanol of Δ H = –900 kJ/mol.

[M_r of ethanol = 46]

The data book value of Δ H for the combustion of ethanol is –1367 kJ/mol.

Give two reasons why the student’s value is much lower than the data book value.

Calculate the bond energy of the C H bond, using information from the equation and the table.

Complete the energy level diagram to show the products and Δ H.

The reaction between hydrogen and chlorine is exothermic.

This is the equation for the reaction.

State the meaning of the term exothermic.

The table gives the bond energies for the H H and H l bonds.

Use the equation and information from the table to calculate the bond energy of

bond energy =_........ kJ / mol

Explain why this reaction is exothermic.

Refer to bond-breaking and bond-making in your answer.

Complete the reaction profile diagram to show the position of the products, the enthalpy change (ΔH) and the activation energy (E_a) for the reaction.

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.

Hydrogen peroxide solution decomposes slowly at room temperature to form water and oxygen.

The equation for the reaction is

A catalyst increases the rate of this reaction.

State one other property of a catalyst.

A student has samples of three solids, X, Y and Z.

The student uses this apparatus to find out which solids act as catalysts in the decomposition of hydrogen peroxide solution.

Describe the method that the student should use to find out which solids act as catalysts.

The decomposition of hydrogen peroxide solution is exothermic.

On the diagram, draw and label the reaction profiles for the reaction

without a catalyst

with a catalyst

The equation for the reaction can be shown using displayed formulae.

The table gives the bond energies for two of the bonds.

Use this information to calculate the total amount of energy needed to break all the bonds in two moles of H₂O₂

Use this information to calculate the total amount of energy released when all the bonds in two moles of H₂O are formed.

Use the value of ΔH and your answers for (i) and (ii) to calculate the bond energy, in kJ/mol, for the O O bond.

bond energy =_........ kJ/mol

The organic compound butadiene is a colourless gas used in the manufacture of synthetic rubber for tyres.

The displayed formula of butadiene is

Explain why butadiene is described as an unsaturated hydrocarbon.

Butadiene reacts with bromine water.

State the colour change that occurs during this reaction.

The equation for the reaction between butadiene and bromine can be shown using displayed formulae.

Br Br Br Br

The table gives some bond energies.

Use this information to calculate the enthalpy change, Δ H, for the reaction.

Include a sign in your answer.

ΔH =_........ kJ/mol

A scientist does an investigation to find out if butadiene would be a good fuel.

He burns a sample of butadiene gas and observes that carbon forms as black soot.

Complete the equation to explain the scientist’s observation.

Explain how one of the products, other than carbon, may cause a problem.

The equation for the combustion of butadiene in excess oxygen is

The enthalpy change for this reaction, Δ H, is – 3446 kJ/mol.

Complete the energy profile diagram for the reaction.

Label the enthalpy change for this reaction, Δ H, and the activation energy.

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]

Oxygen can be prepared from hydrogen peroxide using a catalyst.

Which is a correct statement about oxygen?

Explain how a catalyst increases the rate of a reaction.

The equation for the preparation of oxygen from hydrogen peroxide is

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

The table gives the bond energies for these bonds.

Use the values in the table to calculate the enthalpy change, Δ H, for the reaction.

Include a sign in your answer.

Complete the energy level diagram to show the position of the products and the enthalpy change, Δ H, for the reaction.

This question is about ethane and ethene.

Ethane can be obtained from crude oil.

Describe the industrial process used to separate crude oil into fractions.

The equation for the reaction between ethene gas and hydrogen gas is

The rate of this reaction can be increased by increasing the pressure.

Explain why increasing the pressure increases the rate of this reaction.

The rate of this reaction can also be increased by using a catalyst.

Explain how using a catalyst increases the rate of a reaction.

Give one other way that the rate of reaction between ethene gas and hydrogen gas can be increased.

The reaction between ethene and hydrogen is exothermic.

Complete the reaction profile diagram, including labels for the activation energy and the enthalpy change, H.

The reaction between ethene and hydrogen can be represented using displayed formulae.

H H H H

Use the bond energies in the table to calculate the enthalpy change, H, in kJ/mol for this reaction.

H =_........ kJ/mol

During the Second World War, engineers developed a rocket-powered aircraft.

The aircraft carried these two liquids

• hydrazine, N₂H₄

• hydrogen peroxide, H₂O₂

When these two liquids mix in the combustion chamber, they evaporate and then react rapidly to form nitrogen gas, N₂, and steam, H₂O

The reaction is exothermic.

The equation for the reaction is

The displayed formulae for the reactants and products are

H H

H O H

The tables give the bond energies for the bonds broken in the reactants and the bonds made in the products.

Use the data in the tables to calculate the total amount of energy required to break all of the bonds in the reactants.

Use the data in the tables to calculate the total amount of energy released when all of the bonds in the products are made.

Calculate the enthalpy change, ∆ H, in kJ/mol, for the reaction. Include a sign in your answer.

∆H =_........ 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 N₂H₄ and H₂O₂