Equilibria: past paper questions

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• Question 12May/June 2026, paper 11Multiple choice1 mark

  Nitrogen dioxide dissociates according to the equation shown.

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• Question 12Oct/Nov 2025, paper 11Multiple choice1 mark

  One molecule of haemoglobin, $\text{Hb}$, can bind with four molecules of oxygen according to the equation shown.

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• Question 12Oct/Nov 2024, paper 11Multiple choice1 markHas a diagram

  Lithium reacts with nitrogen at room temperature to form solid ${\text{Li}}_3\text{N}$. Three vessels of equal volume are connected by taps 1 and 2 as shown.

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• Question 12Oct/Nov 2023, paper 11Multiple choice1 markHas a diagram

  Nitrogen dioxide, ${\mathrm{N}\mathrm{O}}_2$, exists in equilibrium with dinitrogen tetroxide, ${\mathrm{N}}_2{\mathrm{O}}_4$.

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• Question 13May/June 2026, paper 11Multiple choice1 markHas a diagram

  Which pH titration curve shows the result of a titration of a strong alkali with a weak acid?

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• Question 13Oct/Nov 2025, paper 11Multiple choice1 markHas a diagram

  Aqueous acid P and aqueous alkali Q have the same concentration. $20{\text{ cm}}^3$ of P is added to a conical flask. Q is slowly added to the flask and the volume of Q and the pH are recorded.

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• Question 13Oct/Nov 2024, paper 11Multiple choice1 mark

  When $0.20\text{ mol}$ of hydrogen gas and $0.15\text{ mol}$ of iodine gas are heated at $723\text{ K}$ until equilibrium is established, the equilibrium mixture contains $0.26\text{ mol}$ of hydrogen iodide. The equation for the reaction is as follows.

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• Question 13Oct/Nov 2023, paper 11Multiple choice1 markHas a diagram

  When an equimolar mixture of ${\mathrm{H}}_2$ and ${\mathrm{I}}_2$ react, the mole fraction of $\mathrm{H}\mathrm{I}$ in the final mixture is $x$. What is the equilibrium constant, $K_p$, for the reaction?

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• Question 14May/June 2026, paper 11Multiple choice1 mark

  Nitrogen and hydrogen react to form ammonia in a reversible reaction. $${\text{N}}_2+3{\text{H}}_2\rightleftharpoons 2{\text{NH}}_3\mathrm{\Delta }H=-92{\text{ kJ mol}}^{-1}$$

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• Question 23Oct/Nov 2025, paper 11Multiple choice1 mark

  Which statement is correct?

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• Question 24Oct/Nov 2024, paper 11Multiple choice1 mark

  Three statements about ammonia molecules and ammonium ions are given. 1 In aqueous solution, ammonia molecules form coordinate bonds with hydroxide ions. 2 Ammonium ions are Brønsted–Lowry acids.

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• Question 15Oct/Nov 2023, paper 12Multiple choice1 mark

  $0.200\text{ mol}$ of sulfur dioxide and $0.200\text{ mol}$ of oxygen are placed in a $1.00{\text{ dm}}^3$ sealed container. The gases are allowed to react until equilibrium is reached.

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• Question 12Oct/Nov 2025, paper 12Multiple choice1 mark

  An equilibrium can be represented by the equation shown. $$\text{P(aq)}+\text{Q(aq)}\rightleftharpoons 2\text{R(aq)}+\text{S(aq)}$$ In a certain mixture, of volume $1.0{\text{ dm}}^3$, the equilibrium concentration of $\text{Q}$ is $10{\text{ mol dm}}^{-3}$.

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• Question 13Oct/Nov 2024, paper 12Multiple choice1 mark

  When some solid ${\mathrm{C}\mathrm{a}}_5({\mathrm{P}\mathrm{O}}_4{)}_3\mathrm{O}\mathrm{H}$ is added to a beaker of water, an equilibrium is set up.

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• Question 17Oct/Nov 2023, paper 12Multiple choice1 markHas a diagram

  The diagram shows a gas syringe with a free-moving piston. The syringe contains gaseous hydrogen, gaseous iodine and gaseous hydrogen iodide at equilibrium. $${\text{H}}_2(\text{g})+{\text{I}}_2(\text{g})\rightleftharpoons 2\text{HI}(\text{g})$$ Three changes are listed.

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• Question 14May/June 2026, paper 12Multiple choice1 mark

  Ethanoic acid dissociates in water. $${\text{CH}}_3\text{COOH}+{\text{H}}_2\text{O}\rightleftharpoons {\text{CH}}_3{\text{COO}}^{-}+{\text{H}}_3{\text{O}}^{+}\mathrm{\Delta }H=-2{\text{ kJ mol}}^{-1}$$ Which change causes the pH of this aqueous solution to decrease?

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• Question 13Oct/Nov 2025, paper 12Multiple choice1 mark

  In the Contact process, sulfur dioxide and oxygen react to form sulfur trioxide. In the Haber process, nitrogen and hydrogen react to form ammonia. Which statement about these processes is correct?

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• Question 14Oct/Nov 2024, paper 12Multiple choice1 mark

  Gaseous hydrogen and gaseous iodine react to form gaseous hydrogen iodide.

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• Question 26Oct/Nov 2023, paper 12Multiple choice1 markHas a diagram

  $\text{NaOH(aq)}$ is added to ${\text{NH}}_4\text{Cl(aq)}$. The mixture is warmed. The gas that is produced turns damp red litmus paper blue.

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• Question 12May/June 2026, paper 13Multiple choice1 mark

  Solid ammonium chloride is heated to a certain temperature in a $0.500{\text{ dm}}^3$ container. Ammonia and hydrogen chloride are formed.

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• Question 13May/June 2026, paper 13Multiple choice1 mark

  When ethanoic acid is mixed with ethanol a reversible reaction occurs. Which statement describes this reaction when it reaches dynamic equilibrium?

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• Question 24May/June 2026, paper 13Multiple choice1 mark

  Ammonium sulfate is heated with calcium hydroxide. Two statements about the reaction are listed. 1 The ammonium ion acts as a base during the reaction.

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• Question 1Oct/Nov 2025, paper 21Structured20 marks

  Chromium, Cr, and its compounds are widely used in many chemical reactions. The most common isotope of Cr is chromium-52. Determine the number of protons, neutrons and electrons in an atom of chromium-52.

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• Question 2Oct/Nov 2023, paper 22Structured15 marksHas a diagram

  NO and ${\mathrm{N}\mathrm{O}}_2$ react at $25{}^{\circ }\mathrm{C}$ to give ${\mathrm{N}}_2{\mathrm{O}}_3$ as shown in the equation.

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• Question 2May/June 2026, paper 21Structured9 marks

  The Contact process uses sulfur to produce sulfuric acid. stage 1 Sulfur is burned in excess air.

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• Question 2Oct/Nov 2025, paper 22Structured20 marksHas a diagram

  The Period 3 elements show trends in physical and chemical properties across the period.

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• Question 13May/June 2024, paper 11Multiple choice1 mark

  An alcohol, $\text{ROH}$, reacts reversibly with ethanoic acid to produce an ester.

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• Question 4May/June 2023, paper 11Multiple choice1 markHas a diagram

  For which equilibrium do both of the equilibrium constants $K_c$ and $K_p$ have no units?

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• Question 3May/June 2026, paper 22Structured8 marks

  Separate samples of $\mathrm{N}\mathrm{a}\mathrm{C}\mathrm{l}$ and $\mathrm{N}\mathrm{a}\mathrm{B}\mathrm{r}$ are reacted with concentrated ${\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_4$. Table 3.1 shows the observations for each reaction. Write an equation for reaction 1.

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• Question 1Oct/Nov 2025, paper 23Structured20 marks

  Chromium, Cr, and its compounds are widely used in many chemical reactions. Cr exists as four stable isotopes. The most common isotope of Cr is chromium-52.

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