Equilibria

During an experiment, $2.00\ \text{mol}$ of hydrogen and $3.00\ \text{mol}$ of iodine were placed in a sealed container, then heated so that the reaction could reach equilibrium at a constant temperature. The container volume was kept at $1.00\ \text{dm}^3$. When equilibrium was reached, the mixture contained $2.40\ \text{mol}$ of iodine. $\text{H}_2\text{(g)} + \text{I}_2\text{(g)} \rightleftharpoons 2\text{HI(g)}$ Calculate the value of the equilibrium constant, $K_c$?

Feb/March 2016

Chlorine gas is commonly used to disinfect polluted water. Which species in the water after chlorine gas has been added is responsible for killing bacteria?

Feb/March 2016

River water from a chalk-rich agricultural region contains $\text{Ca}^{2+}$, $\text{Mg}^{2+}$, $\text{CO}_3^{2-}$, $\text{HCO}_3^-$, $\text{Cl}^-$ and $\text{NO}_3^-\,$ ions. At a water treatment plant, this water is processed by adding a calculated amount of calcium hydroxide. Which substances will precipitate from the river water after the calcium hydroxide has been added?

Feb/March 2016

Once black and white photographic film has been developed, any unreacted silver bromide is eliminated by treatment with sodium thiosulfate. $\text{AgBr} + 2\text{Na}_2\text{S}_2\text{O}_3 \rightarrow 4\text{Na}^+ + \text{Br}^- + [\text{Ag(S}_2\text{O}_3)_2]^{3-}$ What role does the thiosulfate ion play?

Feb/March 2016

Which of the following statements about reversible reactions are correct?

Feb/March 2016

Which reagents, if added in excess, can be used to prepare sodium lactate, CH$_3$CH(OH)CO$_2$Na, from lactic acid, CH$_3$CH(OH)CO$_2$H?

Feb/March 2016

Ammonia is produced from nitrogen and hydrogen by the Haber process. $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)$ What is the expression for $K_c$ for this equilibrium?

Feb/March 2017

A sealed container was charged with two moles of compound P. The container was then heated, causing P to decompose partly to give only Q and R. A dynamic equilibrium involving P, Q and R was set up. When equilibrium was reached, $x$ moles of R were present, and the total number of moles present was $\left(2 + \frac{x}{2}\right)$. What equation represents this reversible reaction?

Feb/March 2017

Sulfur dioxide and oxygen undergo reaction in the gas phase. $2\text{SO}_2(g) + \text{O}_2(g) \\rightleftharpoons 2\text{SO}_3(g) \\qquad \\Delta H = -197\\,\\text{kJ mol}^{-1}$ Which of these statements are correct?

Feb/March 2017

Test-tubes X, Y and Z each hold a small volume of water. A little $\text{NaCl}$ is then put into test-tube X. A little $\text{SiCl}_4$ is then put into test-tube Y. A little $\text{AlCl}_3$ is then put into test-tube Z. After a brief interval, two drops of Universal Indicator solution are placed into each test-tube. Which observations are seen?

Feb/March 2017

$\text{HOCl(aq)}$ is the molecule responsible for killing bacteria when chlorine is added to water. The reaction below forms this molecule. $\text{Cl}_2(g) + \text{H}_2\text{O}(l) \rightleftharpoons \text{HOCl}(aq) + \text{H}^+(aq) + \text{Cl}^-(aq)$ Which statement about this reaction is correct?

Feb/March 2017

Every reactant and product in an exothermic reaction is in the gaseous state. Which statement about this reaction is correct?

Feb/March 2017

The reaction of sulfur dioxide with oxygen is reversible. $2\text{SO}_2 + \text{O}_2 \rightleftharpoons 2\text{SO}_3 \qquad \Delta H^{\circ} = -196\,\text{kJ mol}^{-1}$. At what pressure and temperature would the reaction to the left be preferred?

Feb/March 2018

In which reactions is $\text{NH}_3$ acting as a Brønsted-Lowry acid?

Feb/March 2018

When copper is introduced into a silver-ion solution, the equilibrium below is set up. $\text{Cu}(s) + 2\text{Ag}^+(aq) \rightleftharpoons \text{Cu}^{2+}(aq) + 2\text{Ag}(s) \quad K_c = 1.0 \times 10^5$ What is the equilibrium concentration of silver ions when $[\text{Cu}^{2+}] = 0.10\,\text{mol dm}^{-3}$?

Feb/March 2019

A key stage in the Contact process involves an equilibrium reaction. $2\text{SO}_2 + \text{O}_2 \rightleftharpoons 2\text{SO}_3$ Which row shows the effect of the named condition on the equilibrium yield?

Feb/March 2020

$X$ and $Y$ are oxides of two different Period $3$ elements. When one mole of $X$ is added to water, the resulting solution is neutralised by exactly one mole of $Y$. What might the identities of $X$ and $Y$ be?

Feb/March 2020

Compound Z does not dissolve in water, but it does dissolve at low pH. What might compound Z be?

Feb/March 2020

The reaction equation for silver chloride with aqueous ammonia is given below. $\text{AgCl}(s) + 2\text{NH}_3(aq) \rightleftharpoons [\text{Ag(NH}_3)_2]^+(aq) + \text{Cl}^-(aq)$ State the units of $K_c$ for this reaction.

Feb/March 2020

Methylamine, $\text{CH}_3\text{NH}_2$, shows chemical behaviour similar to that of ammonia, $\text{NH}_3$. When methylamine reacts with hydrogen chloride, it produces a white crystalline salt called methylammonium chloride. $\text{CH}_3\text{NH}_2 + \text{HCl} \rightarrow \text{CH}_3\text{NH}_3^+\text{Cl}^-$ A sample of methylammonium chloride is warmed with aqueous sodium hydroxide. What products are formed?

Feb/March 2021

At $764\,\text{K}$ and $141\,\text{kPa}$, a sample containing $17.15\,\text{mol}\,\text{HI}(g)$ is in dynamic equilibrium with $2.27\,\text{mol}\,\text{H}_2(g)$ and $2.84\,\text{mol}\,\text{I}_2(g)$ in a volume of $1\,\text{m}^3$. $\text{H}_2(g) + \text{I}_2(g) \rightleftharpoons 2\text{HI}(g)$ For this mixture, two equilibrium constants, $K_c$ and $K_p$, can be worked out. Which of the following statements about these equilibrium constants is correct?

Feb/March 2021

A sample with $x\,\text{mol}$ of $\text{Al}_2\text{Cl}_6$ is dissolved in water, producing solution W. To precipitate all of the aluminium as its hydroxide, $y\,\text{mol}$ of sodium hydroxide are needed. Next, more alkali is introduced to make the precipitate dissolve again, forming solution Z. Which of the following statements are correct?

Feb/March 2021

In which reaction does water act as a Brønsted-Lowry base?

Feb/March 2021

Hydrogen and iodine combine to produce hydrogen iodide in an exothermic reaction. The equation is shown. $\text{H}_2(g) + \text{I}_2(g) \rightleftharpoons 2\text{HI}(g)$ At equilibrium, a $1\,\text{m}^3$ reaction vessel contains $\text{H}_2$, $\text{I}_2$ and $\text{HI}$ gases. The temperature is altered so that the total pressure in the $1\,\text{m}^3$ vessel becomes twice as large. What is the effect on the value of $K_p$ and on the position of equilibrium?

Feb/March 2022

Diethylzinc, $(\text{C}_2\text{H}_5)_2\text{Zn}$, is introduced into $\text{NaOH}(aq)$. Two reactions take place. reaction 1 $(\text{C}_2\text{H}_5)_2\text{Zn} + \text{H}_2\text{O} \rightarrow \text{ZnO} + 2\text{C}_2\text{H}_6$ reaction 2 $\text{H}_2\text{O} + \text{ZnO} + 2\text{OH}^- \rightarrow \text{Zn(OH)}_4^{2-}$ For these reactions, which compounds function as Brønsted-Lowry acids?

Feb/March 2022

When ammonia, $\text{NH}_3$, is added to water, only a small amount of ammonium ions, $\text{NH}_4^+$, is produced. Which row is the correct one?

Feb/March 2022

Tartaric acid, $\text{HOOCCH(OH)CH(OH)COOH}$, occurs in many plants. When a sample of tartaric acid is treated with an excess of $\text{LiAlH}_4$, the organic product J is formed. What changes are observed when $\text{NaOH(aq)}$ is added to separate samples of tartaric acid and J?

Feb/March 2023

The table gives the partial pressures in an equilibrium mixture produced by the Haber process. $3\text{H}_2(g) + \text{N}_2(g) \rightleftharpoons 2\text{NH}_3(g)$ What is the value, by number, of the equilibrium constant, $K_p$, for this reaction?

Feb/March 2023

The following reversible reaction is given. $2\text{NOCl}(g) \rightleftharpoons 2\text{NO}(g) + \text{Cl}_2(g) \qquad \Delta H = +77.0\,\text{kJ mol}^{-1}$ Which alteration in conditions would shift the equilibrium position to the right and increase the value of the equilibrium constant?

Feb/March 2023

Nitrogen and hydrogen are combined in a reaction vessel. Equilibrium is then established, producing a gaseous mixture of nitrogen, hydrogen and ammonia. $\text{N}_2 + 3\text{H}_2 \rightleftharpoons 2\text{NH}_3$ At equilibrium, the gas mixture has a total pressure of $300\,\text{atm}$. The amounts present are shown below. Nitrogen: $180$ mol Hydrogen: $590$ mol Ammonia: $160$ mol Calculate the equilibrium constant, $K_p$, for the forward reaction.

Feb/March 2024

A gaseous mixture of hydrogen gas and iodine gas is contained in a reaction vessel with volume $V$ at temperature $T$. The reaction $\text{H}_2 + \text{I}_2 \rightleftharpoons 2\text{HI}$ is then allowed to reach equilibrium. Every substance stays in the gaseous state. Argon gas is next introduced into the reaction vessel. The temperature inside the vessel is kept at $T$. What happens to the rate of the forward reaction and the partial pressure of HI at equilibrium?

Feb/March 2024

Esters may be hydrolysed using an aqueous alkali or an aqueous acid, giving two products. The table compares these two approaches. Which row is correct?

Feb/March 2024

Methanol is produced by the reaction of carbon dioxide with hydrogen. $\text{CO}_2(g) + 3\text{H}_2(g) \rightleftharpoons \text{CH}_3\text{OH}(g) + \text{H}_2\text{O}(g) \qquad \Delta H = -49\,\text{kJ mol}^{-1}$ What change increases the equilibrium yield of methanol for this process?

Feb/March 2025

River water from an agricultural area contains $\text{NH}_4^+$, $\text{CO}_3^{2-}$, $\text{HCO}_3^-$, $\text{Cl}^-$ and $\text{NO}_3^-$ ions. A calculated amount of calcium hydroxide is then added to treat this water. What precipitate is formed when calcium hydroxide is added to the river water?

Feb/March 2025

When an organic acid is mixed with an alcohol, the reaction is reversible and produces an ester together with water. $0.40\,\text{mol}$ of an organic acid and $0.30\,\text{mol}$ of an alcohol are then combined and left at $25^\circ\text{C}$ until equilibrium is achieved. At equilibrium, $0.20\,\text{mol}$ of ester has formed. Calculate the equilibrium constant, $K_c$, for the conditions used?

Feb/March 2025

The table shows the concentrations and pH values for the aqueous solutions of two compounds, X and Y. Either compound may be an acid or a base. For X: concentration $2\,\text{mol dm}^{-3}$, pH $6$. For Y: concentration $2\,\text{mol dm}^{-3}$, pH $9$. Student P concluded that X is a strong acid. Student Q concluded that the extent of dissociation is lower in X(aq) than in Y(aq). Which of the students are correct?

May/June 2010

The water in a swimming pool can be kept free from harmful bacteria by adding aqueous sodium chlorate(I), $\text{NaOCl}$. This then reacts with water to form $\text{HOCl}$ molecules that kill bacteria. $\text{OCl}^-(aq) + \text{H}_2\text{O} \rightleftharpoons \text{OH}^-(aq) + \text{HOCl}(aq)$ Under strong sunlight, the $\text{OCl}^-$ ion is decomposed by ultra-violet light. $\text{OCl}^-(aq) + \text{UV light} \rightarrow \text{Cl}^-(aq) + \tfrac{1}{2}\text{O}_2(g)$ Which method would keep the concentration of $\text{HOCl}(aq)$ at the highest level?

May/June 2010

The percentage of ammonia that could be obtained, if equilibrium was reached in the Haber process, is shown against operating pressure for two temperatures, $400\,^{\circ}\text{C}$ and $500\,^{\circ}\text{C}$. Which diagram shows the two graphs correctly?

May/June 2010

The Haber process used to produce ammonia is shown by the equation below. $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g) \quad \Delta H = -92\ \text{kJ mol}^{-1}$ Which statement is correct for this reaction if the temperature is raised?

May/June 2010

The Haber process used to produce ammonia is shown by the equation below. $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g) \qquad \Delta H = -92\ \text{kJ mol}^{-1}$ Which statement is correct about this reaction if the temperature is raised?

May/June 2010

The percentage of ammonia that could be produced if equilibrium was reached in the Haber process is shown against operating pressure for two temperatures, $400^\text{C}$ and $500^\text{C}$. Which diagram shows the two graphs correctly?

May/June 2010

Pool water can be kept free from harmful bacteria by adding aqueous sodium chlorate(I), $\text{NaOCl}$. It then reacts with water to form $\text{HOCl}$ molecules, which destroy bacteria. $\text{OCl}^-(aq) + \text{H}_2\text{O} \rightleftharpoons \text{OH}^-(aq) + \text{HOCl}(aq)$ Under strong sunlight, the $\text{OCl}^-$ ion is decomposed by ultra-violet light. $\text{OCl}^-(aq) + \text{uv light} \rightarrow \text{Cl}^-(aq) + \tfrac{1}{2}\text{O}_2(g)$ Which method would keep the concentration of $\text{HOCl}(aq)$ at the highest level?

May/June 2010

As organic waste decays in water, carboxylic acids are produced. The water then turns acidic and aquatic organisms are killed. Which additives are appropriate for removing this acid pollution?

May/June 2010

The table shows the concentrations and $\text{pH}$ readings for the aqueous solutions of two compounds, $X$ and $Y$. Each compound may be either an acid or a base. For $X$: concentration $= 2\ \text{mol dm}^{-3}$, $\text{pH} = 6$ For $Y$: concentration $= 2\ \text{mol dm}^{-3}$, $\text{pH} = 9$ Student P decided that $X$ is a strong acid. Student Q decided that the degree of dissociation is smaller in $X(aq)$ than in $Y(aq)$. Which student(s) are correct?

May/June 2010

The table shows the concentrations and pH values for the aqueous solutions of two compounds, $X$ and $Y$. Each compound may be either an acid or a base. Student P decided that $X$ is a strong acid. Student Q decided that the degree of dissociation is smaller in $X(aq)$ than in $Y(aq)$. Which students are right?

May/June 2010

Swimming pool water can be made free from harmful bacteria by adding aqueous sodium chlorate(I), $\text{NaOCl}$. In water, this forms $\text{HOCl}$ molecules, and these kill bacteria. $\text{OCl}^-\text{(aq)} + \text{H}_2\text{O} \rightleftharpoons \text{OH}^-\text{(aq)} + \text{HOCl}\text{(aq)}$ Under bright sunshine, the $\text{OCl}^-$ ion is decomposed by ultra-violet light. $\text{OCl}^-\text{(aq)} + \text{uv light} \rightarrow \text{Cl}^-\text{(aq)} + \tfrac{1}{2}\text{O}_2\text{(g)}$ Which approach would keep the concentration of $\text{HOCl}\text{(aq)}$ at the highest level?

May/June 2010

The proportion of ammonia that could be obtained, provided equilibrium was reached in the Haber process, is shown as a function of operating pressure for two temperatures, $400\,^\circ\text{C}$ and $500\,^\circ\text{C}$. Which diagram is the correct representation of the two graphs?

May/June 2010

As organic refuse decays in water, carboxylic acids are produced. The water becomes acidic and aquatic life is destroyed. Which additives are suitable for removing this acid pollution?

May/June 2010

The Haber process used to produce ammonia is shown by the equation below. $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)$\quad $\Delta H = -92\,\text{kJ mol}^{-1}$ Which statement is true for this reaction if the temperature is raised?

May/June 2010

Which statements are correct under the Brønsted-Lowry theory of acids and bases?

May/June 2011

Which oxides will react with water to form a solution whose pH is $10$ or above?

May/June 2011

In the previous century, the Haber process was sometimes carried out at pressures of $1000\,\text{atm}$ and above. At present, it is usually carried out at pressures below $100\,\text{atm}$. What explains this change?

May/June 2011

In the Contact process, what type of gaseous product is formed, and what catalyst is used?

May/June 2011

The esterification reaction $\text{ethanol} + \text{ethanoic acid} \rightleftharpoons \text{ethyl ethanoate} + \text{water}$ is at equilibrium. The forward reaction is exothermic. In what way can the value of the equilibrium constant $K_c$ be increased?

May/June 2011

Ammonia is produced on a large scale by means of the Haber process. In one specific plant, a temperature of $400\,^{\circ}\text{C}$ and a pressure of $250\,\text{atm}$ are applied together with an iron catalyst. $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g) \qquad \Delta H^{\circ} = -92\,\text{kJ mol}^{-1}$ What change could make the greatest contribution to a higher equilibrium yield of ammonia?

May/June 2011

Which of the following statements are correct according to the Brønsted-Lowry theory of acids and bases?

May/June 2011

During the previous century, the Haber process was occasionally operated at pressures of $1000\ \text{atm}$ and above. Today, it is usually carried out at pressures below $100\ \text{atm}$. What is the reason for this change?

May/June 2011

During sulfuric acid manufacture, the reaction $\text{2SO}_2\text{(g)} + \text{O}_2\text{(g)} \rightleftharpoons \text{2SO}_3\text{(g)}$ is normally carried out at $400\,^{\circ}\text{C}$ and $1\,\text{atm}$ pressure. In an industrial plant, the pressure is altered to $20\,\text{atm}$. What consequences would this change have?

May/June 2012

Initially, 2 moles of compound $P$ were introduced into a vessel. On heating, some of compound $P$ decomposed, and a dynamic equilibrium was set up among chemicals $P$, $Q$ and $R$. When equilibrium was reached, $x$ mol of $R$ were present and the total amount of substance present was $(2 + x)$. What is the equation for this equilibrium?

May/June 2012

Concentrated sulfuric acid acts as a strong acid when it reacts with water. $\text{H}_2\text{SO}_4(\ell) + \text{aq} \rightarrow \text{H}^+(\text{aq}) + \text{HSO}_4^-(\text{aq})$ The ion $\text{HSO}_4^-$ that is produced behaves as a weak acid. $\text{HSO}_4^-(\text{aq}) \rightleftharpoons \text{H}^+(\text{aq}) + \text{SO}_4^{2-}(\text{aq})$ Which of the following statements are correct for $1.0\,\text{mol dm}^{-3}$ sulfuric acid?

May/June 2012

Silver chloride dissolves in aqueous ammonia. What occurs during this process?

May/June 2012

Which of the following statements about the Haber process used to manufacture ammonia are true?

May/June 2012

Initially, two moles of compound P were put into a vessel. The vessel was then heated, causing compound P to decompose partly into Q and R. A dynamic equilibrium was set up among chemicals P, Q and R. When equilibrium was reached, there were $x$ moles of R present, and the total amount of substance present was $(2 + \frac{x}{2})$ moles. What is the equation for this equilibrium reaction?

May/June 2012

Methanol is produced by reacting carbon dioxide with hydrogen. $\text{CO}_2\text{(g)} + 3\text{H}_2\text{(g)} \rightleftharpoons \text{CH}_3\text{OH(g)} + \text{H}_2\text{O(g)} \quad \Delta H = -49\,\text{kJ mol}^{-1}$. Which change would raise the equilibrium yield of methanol in this process?

May/June 2012

A vessel initially contained two moles of compound $P$. When heated, compound $P$ decomposed partially. A dynamic equilibrium involving chemicals $P$, $Q$ and $R$ was then reached. At equilibrium, $x$ mol of $R$ were present, and the overall amount of substance present was $(2 + x)$ mol. What equation represents this equilibrium?

May/June 2012

When BaO, CaO, MgO and SrO are added to water, each of these oxides forms an alkaline solution. Which oxide forms the saturated solution with the greatest pH?

May/June 2012

During sulfuric acid manufacture, the reaction $\text{2SO}_2(g) + \text{O}_2(g) \rightleftharpoons \text{2SO}_3(g)$ is usually carried out at $400\,^{\circ}\text{C}$ and $1\ \text{atm}$ pressure. At one industrial plant, the pressure is changed to $20\ \text{atm}$. What consequences will result from this change?

May/June 2012

Sulfur trioxide is made from sulfur dioxide and oxygen by means of the Contact process. Which condition changes the value of the equilibrium constant, $K_c$?

May/June 2013

The reaction involving sulfur dioxide and oxygen is a dynamic equilibrium. $2\text{SO}_2(g) + \text{O}_2(g) \rightleftharpoons 2\text{SO}_3(g)$ What occurs when the pressure of the system is increased?

May/June 2013

Graphs may be plotted to illustrate the percentage of ammonia present at equilibrium when nitrogen and hydrogen are combined at various temperatures and pressures. Which diagram shows these two graphs correctly?

May/June 2013

For the reaction $\text{H}_2\text{(g)} + \text{I}_2\text{(g)} \rightleftharpoons 2\text{HI(g)}$, the equilibrium constant, $K_c$, is $60$ at $450\,^\circ\text{C}$. How many moles of hydrogen iodide are present at equilibrium with $2$ mol of hydrogen and $0.3$ mol of iodine at $450\,^\circ\text{C}$?

May/June 2014

If equal amounts by volume of saturated barium hydroxide solution and saturated calcium hydroxide solution are combined, a white precipitate, Y, is produced. The resulting mixture is then filtered and carbon dioxide is passed through the filtrate, giving a second white precipitate, Z. What are Y and Z?

May/June 2014

On heating liquid $\text{N}_2\text{F}_4$, it breaks down to form only one product, X. Which statements are correct?

May/June 2014

The Brønsted-Lowry theory explains how acids and bases are identified. If concentrated sulfuric acid is combined with concentrated nitric acid, the following reactions take place. $\text{H}_2\text{SO}_4 + \text{HNO}_3 \rightleftharpoons \text{HSO}_4^- + \text{H}_2\text{NO}_3^+$ $\text{H}_2\text{NO}_3^+ \rightleftharpoons \text{H}_2\text{O} + \text{NO}_2^+$ $\text{H}_2\text{O} + \text{H}_2\text{SO}_4 \rightleftharpoons \text{HSO}_4^- + \text{H}_3\text{O}^+$ Which species function as bases in these reactions?

May/June 2014

A test-tube containing HI gas and a test-tube containing HBr gas are put together in surroundings at temperature, $T$. Which sets of observations could occur, depending on the temperature, $T$?

May/June 2014

The Contact process is employed in the production of sulfuric acid. The equation for the main reaction is shown below. $2\text{SO}_2\text{(g)} + \text{O}_2\text{(g)} \rightleftharpoons 2\text{SO}_3\text{(g)} \qquad \Delta H = -196\,\text{kJ mol}^{-1}$ Which statement concerning this reaction is not correct?

May/June 2014

$X$ and $Y$ are oxides of two different Period 3 elements. When one mole of $Y$ is mixed with water, the resulting solution is neutralised by exactly one mole of $X$. What might the identities of $X$ and $Y$ be?

May/June 2014

Sulfuric acid counts as a Brønsted-Lowry acid. In which of these reactions is sulfuric acid acting as an acid?

May/June 2014

Silver chloride dissolves in aqueous ammonia. What occurs during this process?

May/June 2014

A car is fitted with a catalytic converter in its exhaust system. When the exhaust gases are analysed, they are found to contain small amounts of nitrogen oxides. Which changes would lead to lower concentrations of nitrogen oxides in the exhaust?

May/June 2014

Hydrogen gas and carbon dioxide gas are present in equal molar quantities at $800\,\text{K}$. A reversible reaction occurs. $\text{H}_2(g) + \text{CO}_2(g) \rightleftharpoons \text{H}_2\text{O}(g) + \text{CO}(g)$ When equilibrium is reached, the partial pressures of $\text{H}_2$ and $\text{CO}_2$ are each $10.0\,\text{kPa}$. At $800\,\text{K}$, $K_p$ is $0.288$. Calculate the partial pressure of $\text{CO}$ in the equilibrium mixture.

May/June 2014

A dynamic equilibrium is reached when methane produces hydrogen and ethyne, $\text{C}_2\text{H}_2$. $2CH_4(g) \rightleftharpoons 3H_2(g) + C_2H_2(g)$ What are the units of $K_c$?

May/June 2014

Which of these reactions has to be heated in order to produce a solid product?

May/June 2014

Chlorine is used extensively in water treatment plants. What reaction occurs when chlorine dissolves in water?

May/June 2015

Which statements concerning the industrial production of sulfuric acid are correct?

May/June 2015

A sealed flask with a volume of $1\,\text{dm}^3$ is used to heat one mole of phosphorus(V) chloride, $\text{PCl}_5$, to $600\,\text{K}$. Once equilibrium has been reached, measurements are recorded. $\text{PCl}_5(g) \rightleftharpoons \text{PCl}_3(g) + \text{Cl}_2(g)$ The experiment is then carried out again, but this time one mole of phosphorus(V) chloride is heated to $600\,\text{K}$ in a sealed flask of volume $2\,\text{dm}^3$. How will the measurements vary?

May/June 2015

In which reaction does the underlined substance function as a base?

May/June 2015

A single molecule of haemoglobin, $\text{Hb}$, is able to combine with four molecules of oxygen, as shown by the equation below. $\text{Hb(aq)} + 4\text{O}_2(aq) \rightleftharpoons \text{Hb(O}_2)_4(aq)$ At equilibrium, when the concentration of $\text{O}_2$ is $7.6 \times 10^{-6}\,\text{mol dm}^{-3}$, the equilibrium concentrations of $\text{Hb}$ and $\text{Hb(O}_2)_4$ are the same. What is the value of $K_c$ for this equilibrium?

May/June 2015

Photochromic glass, which is used in sunglasses, turns darker when it is exposed to intense light and becomes clearer again when the light intensity decreases. The degree of darkening depends on the concentration of silver atoms. The reactions below are involved. Reaction 1: $\text{Ag}^+ + \text{Cl}^- \rightleftharpoons \text{Ag} + \text{Cl}$ Reaction 2: $\text{Cu}^+ + \text{Cl} \rightarrow \text{Cu}^{2+} + \text{Cl}^-$ Reaction 3: $\text{Cu}^{2+} + \text{Ag} \rightarrow \text{Cu}^+ + \text{Ag}^+$ Which statement about these reactions is correct?

May/June 2015

Lactic acid is found naturally, for instance in sour milk. What is one property of lactic acid?

May/June 2015

Nitrogen dioxide, $\text{NO}_2$, is in equilibrium with dinitrogen tetroxide, $\text{N}_2\text{O}_4$. $2\text{NO}_2(g) \rightleftharpoons \text{N}_2\text{O}_4(g)$, $\Delta H = -57\text{ kJ mol}^{-1}$ Which conditions lead to the largest percentage of $\text{N}_2\text{O}_4(g)$ at equilibrium?

May/June 2015

When a sample of $\text{HI}$ is heated to a specific temperature, the equilibrium shown below is attained. $2\text{HI}(g) \rightleftharpoons \text{H}_2(g) + \text{I}_2(g)$ At this temperature, the partial pressure of $\text{HI}(g)$ is $28$ times that of $\text{H}_2(g)$. Determine the value of $K_p$ at this temperature?

May/June 2015

Two different tests were performed on an aqueous solution of a salt that has only two ions. After each test, the mixtures formed were filtered and the filtrate was collected. Test 1: adding aqueous silver nitrate acidified with dilute nitric acid produces a yellow precipitate, giving filtrate solution $P$. Test 2: adding dilute sulfuric acid produces a white precipitate, giving filtrate solution $Q$. Which ions are present in the filtrates?

May/June 2015

Ester P has a fruity smell and is shown by the structural formula below. $\text{CH}_3\text{COOCH}_2\text{CH}_2\text{CH}(\text{CH}_3)_2$ Which compounds are formed when P is hydrolysed using hydrochloric acid?

May/June 2015

The chemical equation for the reaction of carbon monoxide with hydrogen is given below. $\text{CO}(g) + 3\text{H}_2(g) \rightleftharpoons \text{CH}_4(g) + \text{H}_2\text{O}(g)$ What are the units of $K_p$ for this reaction?

May/June 2016

In certain areas, lime, $\text{Ca(OH)}_2$, is mixed into soil to help crops grow better. Which statement correctly explains why lime improves crop growth?

May/June 2016

Aqueous solution was made by dissolving a blend of $1.0\,\text{mol}$ of $\text{AgNO}_3$ and $1.0\,\text{mol}$ of $\text{FeSO}_4$ in $1.00\,\text{dm}^3$ of water. After equilibrium had been reached, the mixture contained $0.44\,\text{mol}$ of $\text{Ag}^+(aq)$. $\text{Ag}^+(aq) + \text{Fe}^{2+}(aq) \rightleftharpoons \text{Ag}(s) + \text{Fe}^{3+}(aq)$ Determine the numerical value of $K_c$?

May/June 2016

At a particular temperature, solid ammonium chloride breaks down in a $0.500\,\text{dm}^3$ vessel to produce ammonia and hydrogen chloride. $\text{NH}_4\text{Cl}(s) \rightleftharpoons \text{NH}_3(g) + \text{HCl}(g)$ The starting amount of ammonium chloride was $1.00\,\text{mol}$, and after equilibrium was established, $0.300\,\text{mol}$ of ammonium chloride remained. Calculate the numerical value of $K_c$ for this reaction under these conditions?

May/June 2016

Ammonia gas, $\text{NH}_3$, combines with hydrogen sulfide gas, $\text{H}_2\text{S}$, to make the salt ammonium sulfide, $(\text{NH}_4)_2\text{S}$. When ammonium sulfide dissolves in water, an orange alkaline solution is produced. $(\text{NH}_4)_2\text{S}(aq) \rightleftharpoons \text{NH}_3(aq) + \text{NH}_4\text{SH}(aq)$ Adding $\text{NaOH}(aq)$ to this solution gives off a gas, $X$. Adding $\text{HCl}(aq)$ to a different portion of the solution produces a gas, $Y$. Which gases are $X$ and $Y$?

May/June 2016

In this question, it may be assumed that all gases behave ideally. A chemist heats a mixture of nitrogen and oxygen gases in a sealed container at constant temperature until the system attains a dynamic equilibrium containing $\text{N}_2(g)$, $\text{O}_2(g)$ and $\text{NO}(g)$. $\text{N}_2(g) + \text{O}_2(g) \rightleftharpoons 2\text{NO}(g)$ The chemist carries out the experiment again at the same temperature, with the same initial amounts of $\text{N}_2(g)$ and $\text{O}_2(g)$, but under a much greater pressure. Which statements about the second experiment at higher pressure are correct?

May/June 2016