Reversible reactions and equilibrium

Two reactions that involve water are illustrated below. X: anhydrous cobalt(II) chloride $\rightarrow$ hydrated cobalt(II) chloride Y: iron + oxygen + water $\rightarrow$ rust Which of these reactions can be reversed by heating?

Feb/March 2016

A reversible reaction is represented below. $2\text{NO}_2(\text{g}) \rightleftharpoons \text{N}_2\text{O}_4(\text{g}) \qquad \Delta H = -58\,\text{kJ mol}^{-1}$ Which statement concerning an equilibrium mixture containing $\text{NO}_2$ and $\text{N}_2\text{O}_4$ is correct?

Feb/March 2016

The equation showing the action of heat on hydrated sodium carbonate is given below. $\text{Na}_2\text{CO}_3\cdot 10\text{H}_2\text{O}(s) \rightleftharpoons \text{Na}_2\text{CO}_3(s) + 10\text{H}_2\text{O}(g)$ Four students have each made a statement about this reaction. Which students’ statements are correct?

Feb/March 2017

The equation for the reversible reaction of hydrogen with iodine to produce hydrogen iodide is given. The colours of the reactants and products are shown. $\text{H}_2(g) + \text{I}_2(g) \rightleftharpoons 2\text{HI}(g)$. The forward reaction releases heat. Which statement is correct?

Feb/March 2017

Ammonia is made by reacting nitrogen with hydrogen at high temperature and pressure. $\text{N}_2 + 3\text{H}_2 \rightleftharpoons 2\text{NH}_3$

Feb/March 2017

Nitryl chloride, $\text{NO}_2\text{Cl}$, reacts with nitric oxide, NO, and the forward change gives out heat. $\text{NO}_2\text{Cl}$(g) + NO(g) $\rightleftharpoons$ $\text{NO}_2$(g) + NOCl(g) This reaction is able to establish equilibrium.

Feb/March 2017

Methanol is formed when carbon monoxide reacts with hydrogen. This reaction is reversible. $\text{CO}(g) + 2\text{H}_2(g) \rightleftharpoons \text{CH}_3\text{OH}(g)$ The forward reaction releases heat. Which combination of temperature and pressure results in the greatest equilibrium yield of methanol?

Feb/March 2018

The reaction equation for making sulfur trioxide from sulfur dioxide is shown below. $2\text{SO}_2(g) + \text{O}_2(g) \rightleftharpoons 2\text{SO}_3(g)$ The forward reaction releases heat. Which pairing of pressure and temperature gives the greatest equilibrium yield of sulfur trioxide?

Feb/March 2018

Which reaction can be reversed?

Feb/March 2019

Which reaction can be reversed?

Feb/March 2019

A gas syringe was charged with some nitrogen dioxide gas. The syringe tip is then sealed. A reversible reaction takes place and eventually equilibrium is established: $2\text{NO}_2(\text{g}) \rightleftharpoons \text{N}_2\text{O}_4(\text{g})$. The forward reaction is exothermic. Which statement about this reaction is correct?

Feb/March 2019

An equilibrium equation is given: $\text{N}_2\text{O}_4(\text{g}) \rightleftharpoons 2\text{NO}_2(\text{g})$. The forward reaction absorbs heat. How do temperature and pressure changes affect the equilibrium position?

Feb/March 2020

The question concerns ammonia.

Feb/March 2021

The reversible reaction shown occurs in a closed system at fixed temperature. $\text{P}(g) + \text{Q}(g) + \text{R}(g) \rightleftharpoons \text{S}(g) + \text{T}(g)$ Once the reaction has attained equilibrium, extra T is introduced. After T is added, which other substances have an increase in concentration?

Feb/March 2023

The Haber process is the method used to produce ammonia.

Feb/March 2023

Which reaction can be reversed?

Feb/March 2024

Within the Haber process, nitrogen is combined with hydrogen to form ammonia. $\text{N}_2(\text{g}) + 3\text{H}_2(\text{g}) \rightleftharpoons 2\text{NH}_3(\text{g})$ This forward reaction gives out heat. Which conditions will give the highest yield of ammonia?

Feb/March 2024

The reaction between methanoic acid and ethanol, in the presence of a catalyst, is shown by the equation below. HCOOH + CH3CH2OH ⇌ X + H2O ΔH = -29.5 kJ/mol X is the ester that is produced.

Feb/March 2024

The equation for the reaction between ammonia and oxygen is given below. $4\text{NH}_3(g) + 5\text{O}_2(g) \rightleftharpoons 4\text{NO}(g) + 6\text{H}_2\text{O}(g) \quad \Delta H = -909\,\text{kJ mol}^{-1}$ Which two alterations to the reaction conditions will both shift the equilibrium position to the right?

Feb/March 2025

Carbonyl chloride, COCl₂, is made by reacting carbon monoxide with chlorine. $\text{CO(g)} + \text{Cl}_2(\text{g}) \rightleftharpoons \text{COCl}_2(\text{g}) \quad \Delta H = -105\,\text{kJ/mol}$ This reaction is carried out in a closed system until equilibrium is established. The conditions used are 200 ^{\circ}C and 200 kPa.

Feb/March 2025

Which reaction can be reversed?

May/June 2016

Steam undergoes reaction with carbon in an endothermic process. $\text{C}(s) + \text{H}_2\text{O}(g) \rightleftharpoons \text{CO}(g) + \text{H}_2(g)$. Which temperature and pressure conditions would produce the greatest yield of hydrogen?

May/June 2016

Ammonia is produced in a reversible reaction. $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)$ The forward reaction is exothermic. Which changes in conditions would raise the yield of ammonia?

May/June 2016

Methanol is produced when carbon monoxide reacts with hydrogen. This reaction is exothermic and reaches chemical equilibrium. The reaction equation is $\text{CO}(g) + 2\text{H}_2(g) \rightleftharpoons \text{CH}_3\text{OH}(g)$. Which changes in temperature and pressure would increase the yield of methanol?

May/June 2016

Ammonia is made by a reversible reaction. $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)$ The forward reaction is exothermic. What effect does increasing the pressure have on the percentage yield and the rate of formation of ammonia?

May/June 2016

The Contact process is employed in the production of sulfuric acid. Which statement about this process is not correct?

May/June 2016

Methanol is made by allowing carbon monoxide and hydrogen to react in the presence of an aluminium oxide catalyst. The reaction equation is $\text{CO(g)} + 2\text{H}_2\text{(g)} \rightleftharpoons \text{CH}_3\text{OH(g)}$. This reaction is reversible, and the forward reaction is exothermic. Which alteration to the conditions would increase the yield of methanol?

May/June 2016

Ammonia is made by the Haber process. $\text{N}_2(\text{g}) + 3\text{H}_2(\text{g}) \rightarrow 2\text{NH}_3(\text{g})$. Which statement about the Haber process is incorrect?

May/June 2016

Ammonia is made when nitrogen reacts with hydrogen in the presence of a catalyst.

May/June 2016

Sulfur dioxide reacts with excess oxygen to produce sulfur trioxide. $\text{2SO}_2(g) + \text{O}_2(g) \rightleftharpoons \text{2SO}_3(g)$

May/June 2016

Ethanol may be produced by allowing ethene to react with steam. $\text{C}_2\text{H}_4(\text{g}) + \text{H}_2\text{O(g}) \rightleftharpoons \text{C}_2\text{H}_5\text{OH(g})$

May/June 2016

Nitrogen, hydrogen and ammonia gases are put into a container. The container is then sealed. After a period of time, equilibrium is established. $\text{N}_2\text{(g)} + 3\text{H}_2\text{(g)} \rightleftharpoons 2\text{NH}_3\text{(g)}$ Which statement gives the description of the equilibrium in this container?

May/June 2017

Which row shows the conditions for the Haber process?

May/June 2017

The process used to produce ammonia from nitrogen and hydrogen is reversible. An equilibrium may be set up between ammonia, nitrogen and hydrogen. Which statement describes this equilibrium?

May/June 2017

Which statement about the conditions used in the Haber process is incorrect?

May/June 2017

Hydrogen is formed when methane reacts with steam. The reaction is represented by the equation below. $\text{CH}_4(\text{g}) + \text{H}_2\text{O}(\text{g}) \rightleftharpoons \text{CO}(\text{g}) + 3\text{H}_2(\text{g})$ The forward reaction is endothermic in nature. Which conditions would give the greatest yield of hydrogen?

May/June 2017

This question focuses on nitrogen and several of its compounds.

May/June 2017

Sulfur trioxide is formed in this reversible reaction: $2\text{SO}_2\text{(g)} + \text{O}_2\text{(g)} \rightleftharpoons 2\text{SO}_3\text{(g)}$. The forward reaction is exothermic. Under what conditions is the equilibrium yield of sulfur trioxide greatest?

May/June 2018

Ammonia is produced by combining hydrogen with nitrogen in the Haber process. Which row gives the sources of hydrogen and nitrogen and the conditions used to produce ammonia in the Haber process?

May/June 2018

At 2 atmospheres pressure, sulfur dioxide reacts with oxygen. The forward reaction is exothermic, so heat is released. The reaction equation is given below. $2\text{SO}_2(g) + \text{O}_2(g) \rightleftharpoons 2\text{SO}_3(g)$ The mixture reaches equilibrium. The pressure is then doubled. How does the amount of sulfur trioxide produced change, and why?

May/June 2018

Within the Contact process, sulfur dioxide is changed into sulfur trioxide in a reversible reaction. $2\text{SO}_2(g) + \text{O}_2(g) \rightleftharpoons 2\text{SO}_3(g)$ This forward reaction is exothermic. What conditions produce the greatest equilibrium yield of sulfur trioxide?

May/June 2018

Ammonia is produced by combining hydrogen with nitrogen in the Haber process. Which row shows the sources of hydrogen and nitrogen and the conditions employed in the production of ammonia in the Haber process?

May/June 2018

Hydrogen and iodine undergo a reversible reaction and hydrogen iodide is produced. $\text{H}_2(g) + \text{I}_2(g) \rightleftharpoons 2\text{HI}(g)$. The forward reaction gives out heat. A sealed gas syringe containing an equilibrium mixture of hydrogen, iodine and hydrogen iodide gases was heated to 250^{\circ}C. The equilibrium mixture appeared pale purple.

May/June 2018

If blue-green crystals of nickel(II) sulfate are heated, water is given off and a yellow solid is left behind. When water is then added to the yellow solid, the blue-green colour comes back. Which process is shown by these changes?

May/June 2019

The graph illustrates how the product yield in a reversible reaction varies when temperature and pressure are altered. Every reactant and product is a gas. $\text{reactants} \; \rightleftharpoons \; \text{products}$ Which row gives the correct answer for this reversible reaction?

May/June 2019

Ammonia is made using the Haber Process. $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)$ Because the forward reaction gives out heat, which conditions will give the greatest yield of ammonia?

May/June 2019

Which row indicates the conditions applied in the Contact process?

May/June 2019

If blue-green crystals of nickel(II) sulfate are heated, water is given off and a yellow solid is left behind. When water is then added to the yellow solid, the blue-green colour comes back. Which process describes these changes?

May/June 2019

The reaction equation for making ethanol is shown below. $\text{C}_2\text{H}_4(g) + \text{H}_2\text{O}(g) \rightleftharpoons \text{C}_2\text{H}_5\text{OH}(g)$ How does doubling the pressure affect this reaction?

May/June 2019

Ammonia is made in the Haber process. The reaction equation is given below. $3\text{H}_2(\text{g}) + \text{N}_2(\text{g}) \rightleftharpoons 2\text{NH}_3(\text{g})$ The forward reaction gives out heat. Which temperature and pressure conditions give the greatest yield of ammonia?

May/June 2019

A reaction between nitrogen and oxygen is illustrated below. The forward reaction absorbs energy. $\text{N}_2(g) + \text{O}_2(g) \rightleftharpoons 2\text{NO}(g)$ Which alteration will raise the equilibrium yield of nitrogen monoxide, NO?

May/June 2019

Ammonia is produced in an exothermic reaction. $\text{N}_2(\text{g}) + 3\text{H}_2(\text{g}) \rightleftharpoons 2\text{NH}_3(\text{g})$ What effect does a lower temperature have on the speed of ammonia formation and on the equilibrium yield of ammonia?

May/June 2019

Which row gives the conditions used in the Contact process?

May/June 2019

This equation shows a reaction that may be reversed by altering the conditions. anhydrous cobalt(II) chloride + water $\rightleftharpoons$ hydrated cobalt(II) chloride. Which of the following statements is correct?

May/June 2021

Which of the following statements about a reaction at equilibrium is correct?

May/June 2021

Ammonia is produced in the Haber process by combining nitrogen with hydrogen. The equation for the process is shown: $N_2 + 3H_2 \rightleftharpoons 2NH_3$. Which changes to the reaction conditions would result in a higher yield of ammonia?

May/June 2021

What catalyst is used in the Contact process?

May/June 2021

When bismuth(III) chloride, $\text{BiCl}_3$, reacts with water, white bismuth(III) oxychloride, $\text{BiOCl}$, is produced. The reaction is represented by the equation. $\text{BiCl}_3\text{(aq)} + \text{H}_2\text{O(l)} \rightleftharpoons \text{BiOCl(s)} + 2\text{H}^+\text{(aq)} + 2\text{Cl}^-\text{(aq)}$. This reaction is in equilibrium. Which changes make the white precipitate dissolve?

May/June 2021

The Haber process is used to make ammonia. State the conditions used in the Haber process.

May/June 2021

Ammonia is produced from nitrogen and hydrogen. The reaction equation is shown below. $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)$ The forward reaction is exothermic. Which conditions would result in the highest equilibrium yield of ammonia?

May/June 2021

In the Contact process, which substance is used as the catalyst for manufacturing sulfuric acid?

May/June 2021

Dinitrogen tetroxide, N$_2$O$_4$, breaks down to form nitrogen dioxide, NO$_2$. This reaction can go in both directions. $\text{N}_2\text{O}_4(g) \rightleftharpoons 2\text{NO}_2(g)$ (colourless gas ⇌ brown gas). A gas syringe holding a mixture of dinitrogen tetroxide and nitrogen dioxide gases was sealed and then heated. Once equilibrium was reached, the mixture had a pale brown colour.

May/June 2021

Hydrogen iodide, HI, breaks down into iodine and hydrogen, and the reaction can proceed in both directions. $\text{2HI(g)} \rightleftharpoons \text{I}_2\text{(g)} + \text{H}_2\text{(g)}$ A sealed gas syringe held a mixture of hydrogen iodide, iodine and hydrogen gases. When equilibrium was reached, the mixture had a pale purple colour.

May/June 2021

The equation for producing ammonia by the Haber process is shown below. $3\text{H}_2(g) + \text{N}_2(g) \rightleftharpoons 2\text{NH}_3(g)$ The forward reaction releases heat. Which row shows the effect of the change stated on the rate of reaction and the yield of ammonia?

May/June 2022

When the colourless gas $\text{N}_2\text{O}_4$ is heated, it produces the brown gas $\text{NO}_2$. As the reaction mixture is cooled, the brown colour disappears and changes back to colourless. Which type of reaction is shown by these observations?

May/June 2022

In the Contact process, which reaction uses a catalyst?

May/June 2022

Within the Contact process, sulfur dioxide is changed into sulfur trioxide. $2\text{SO}_2(g) + \text{O}_2(g) \rightleftharpoons 2\text{SO}_3(g)$. What effect does a decrease in pressure have on the rate at which sulfur trioxide forms and on the percentage yield of sulfur trioxide at equilibrium?

May/June 2022

Ethanoic acid is made by reacting methanol with carbon monoxide. This gives an equilibrium mixture. $\text{CH}_3\text{OH}(g) + \text{CO}(g) \rightleftharpoons \text{CH}_3\text{COOH}(g)$

May/June 2022

Which reaction can be reversed?

May/June 2023

In the Contact process, sulfur dioxide reacts with oxygen to produce sulfur trioxide. Which conditions are used for this reaction?

May/June 2023

Which reaction can be reversed?

May/June 2023

Which row indicates the conditions used in the Contact process?

May/June 2023

This question concerns sulfur and sulfur compounds. Sulfur is changed into sulfuric acid, H$_2$SO$_4$, by the Contact process. The process has four stages: stage 1 Molten sulfur is changed into sulfur dioxide. stage 2 Sulfur dioxide reacts with oxygen to make sulfur trioxide. stage 3 Sulfur trioxide joins with concentrated sulfuric acid to produce oleum, H$_2$S$_2$O$_7$. stage 4 Oleum reacts to produce concentrated sulfuric acid.

May/June 2023

More than 200 million tonnes of sulfuric acid are manufactured each year.

May/June 2023

This question concerns nitrogen and compounds of nitrogen.

May/June 2023

Hydrogen is produced when carbon reacts with steam. The reaction is represented by the equation below. $\text{C}(s) + \text{H}_2\text{O}(g) \rightleftharpoons \text{H}_2(g) + \text{CO}(g)$ The forward reaction absorbs heat. Which row gives the pressure and temperature changes that would both move the equilibrium position to the right?

May/June 2024

Which row indicates the conditions used to convert sulfur dioxide into sulfur trioxide in the Contact process?

May/June 2024

The equation shows the reversible reaction between ethene and steam. $\text{C}_2\text{H}_4(g) + \text{H}_2\text{O}(g) \rightleftharpoons \text{C}_2\text{H}_5\text{OH}(g)$ \qquad $\Delta H$ is negative Which row gives the conditions that result in the highest yield of ethanol?

May/June 2024

Which row gives the pressure and catalyst used for converting sulfur dioxide into sulfur trioxide in the Contact process?

May/June 2024

The Contact process is employed to change sulfur dioxide into sulfur trioxide. Vanadium(V) oxide acts as the catalyst in this process. $2\text{SO}_2\text{(g)} + \text{O}_2\text{(g)} \rightarrow 2\text{SO}_3\text{(g)}$ The forward reaction in this equilibrium gives out heat. Which of the statements about this process are correct?

May/June 2024

Nitrogen combines with hydrogen to produce ammonia when an iron catalyst is present. This reaction can proceed in both directions. $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)$ Which statement about this reaction is correct?

May/June 2024

Hydrogen iodide undergoes thermal decomposition to form iodine and hydrogen, and the process is reversible. $2\text{HI(g)} \rightleftharpoons \text{I}_2\text{(g)} + \text{H}_2\text{(g)}$ Fig. 4.1 shows a sealed gas syringe holding a mixture of hydrogen iodide, iodine and hydrogen gases. The syringe is sealed and the mixture is heated to $300\ ^\circ\text{C}$. At equilibrium, the gas mixture is purple.

May/June 2024

The displayed symbol equation for the industrial manufacture of ammonia is: $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g) \quad \Delta H = -90\,\text{kJ/mol}$

May/June 2024

Dinitrogen tetroxide, N₂O₄, breaks down to nitrogen dioxide, NO₂. This is a reversible reaction. $\text{N}_2\text{O}_4(g) \rightleftharpoons 2\text{NO}_2(g)$ Fig. 4.1 shows a sealed gas syringe that contains a mixture of dinitrogen tetroxide and nitrogen dioxide. The gas syringe is sealed. The mixture reaches equilibrium and the gases are a pale brown.

May/June 2024

The equation for the reaction between sulfur dioxide and oxygen is shown. $2\text{SO}_2 + \text{O}_2 \rightleftharpoons 2\text{SO}_3$ What does the symbol $\rightleftharpoons$ mean?

May/June 2025

Industrially, ammonia is produced by the Haber process. The equation is shown. $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g) \quad \Delta H = -92\,\text{kJ mol}^{-1}$ The conditions employed are $450^{\circ}\text{C}$ and $200\,\text{atm}$. Which of the following statements about these conditions are correct?

May/June 2025

Which row gives the conditions employed in the industrial manufacture of sulfuric acid by the Contact process?

May/June 2025

The reaction between aqueous iron(III) ions, $\text{Fe}^{3+}$(aq), and aqueous thiocyanate ions, $\text{SCN}^-$(aq), is reversible. Its equation is $\text{Fe}^{3+}(aq) + \text{SCN}^-(aq) \rightleftharpoons \text{FeSCN}^{2+}(aq)$. When equilibrium is reached, the concentrations of $\text{Fe}^{3+}$ ions, $\text{SCN}^-$ ions, and $\text{FeSCN}^{2+}$ ions are identical, and the mixture is orange in colour. If a few drops of aqueous thiocyanate ions are then added to the mixture, a new equilibrium is established. How does the colour of the mixture change?

May/June 2025

Methanol, CH$_3$OH, is made by reacting hydrogen with carbon monoxide. An equilibrium mixture results. $2\text{H}_2(g) + \text{CO}(g) \rightleftharpoons \text{CH}_3\text{OH}(g)$

May/June 2025

Ethanoic acid is produced when methanol reacts with carbon monoxide. An equilibrium mixture results. $CH_3OH(g) + CO(g) \rightleftharpoons CH_3COOH(g)$

May/June 2025

Which reaction can proceed in both directions?

Oct/Nov 2016

The reversible reaction below occurs in a sealed container at fixed temperature. $\text{P(g)} + \text{Q(g)} + \text{R(g)} \rightleftharpoons \text{S(g)} + \text{T(g)}$ Once equilibrium is established, extra $\text{T}$ is introduced. Following the addition of $\text{T}$, which substances have an increase in concentration?

Oct/Nov 2016

Ammonia is produced using the Haber process. This reaction is exothermic. $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g) \qquad \Delta H = -92\,\text{kJ mol}^{-1}$ Which statement concerning the Haber process is correct?

Oct/Nov 2016

When the reaction between hydrogen and iodine has reached equilibrium at $400^\circ\text{C}$, the reaction is exothermic. $\text{H}_2(g) + \text{I}_2(g) \rightleftharpoons 2\text{HI}(g) \qquad \Delta H = -13\,\text{kJ mol}^{-1}$ Which change in conditions would increase the percentage of hydrogen iodide in the equilibrium mixture?

Oct/Nov 2016

Ammonia is produced by the Haber process with the use of an iron catalyst. $\text{N}_2 + 3\text{H}_2 \rightleftharpoons 2\text{NH}_3$ A 100% yield cannot be achieved. What is the reason for this?

Oct/Nov 2016

Sulfuric acid is produced through a sequence of chemical reactions, and one of these is catalysed by vanadium(V) oxide. What is the equation for the reaction that is catalysed by vanadium(V) oxide?

Oct/Nov 2016

Chlorine may be produced using the reaction below. This reaction is exothermic. $\text{4HCl(g)} + \text{O}_2\text{(g)} \rightleftharpoons \text{2H}_2\text{O(g)} + \text{2Cl}_2\text{(g)}$. Which alteration increases the equilibrium yield of chlorine?

Oct/Nov 2016

In the Haber process used to produce ammonia, the conditions are $450^\circ\text{C}$ and $250$ atmospheres. Nitrogen and hydrogen are fed in a $1":"3$ ratio by volume. This reaction releases heat. $\text{N}_2\text{(g)} + 3\text{H}_2\text{(g)} \rightleftharpoons 2\text{NH}_3\text{(g)} \quad \Delta H = -92\,\text{kJ mol}^{-1}$. Which change would lead to a higher yield of ammonia?

Oct/Nov 2016

The diagram below illustrates four stages in the conversion of sulfur into sulfuric acid. At which stage is a catalyst used?

Oct/Nov 2016

Lime (calcium oxide) is produced by heating limestone (calcium carbonate). $\text{CaCO}_3(s) \rightleftharpoons \text{CaO}(s) + \text{CO}_2(g)$

Oct/Nov 2016