Chemical equilibria: reversible reactions, dynamic equilibrium: 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 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 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 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 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 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 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 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 14Oct/Nov 2024, paper 12Multiple choice1 mark

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

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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 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 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 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 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 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 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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• 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 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 3May/June 2026, paper 23Structured13 marksHas a diagram

  The conditions used for the conversion of sulfur dioxide to sulfur trioxide in the Contact process are carefully controlled.

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• Question 9May/June 2025, paper 11Multiple choice1 markHas a diagram

  An aqueous solution X contains substance HQ which behaves as a weak acid.

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• Question 14May/June 2024, paper 11Multiple choice1 markHas a diagram

  Graphs can be drawn to show the percentage of ammonia at equilibrium when nitrogen and hydrogen are mixed at different temperatures and pressures.

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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 10May/June 2025, paper 11Multiple choice1 mark

  Dinitrogen tetroxide, ${\text{N}}_2{\text{O}}_4$, decomposes reversibly.

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• Question 13May/June 2024, paper 12Multiple choice1 markHas a diagram

  The volume of ammonia produced against time is measured in two experiments.

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• Question 8May/June 2023, paper 11Multiple choice1 mark

  The Contact process takes place at a pressure between $100000\mathrm{P}\mathrm{a}$ and $200000\mathrm{P}\mathrm{a}$.

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• Question 4May/June 2025, paper 12Multiple choice1 mark

  The reaction between sulfur dioxide and oxygen has the equation shown.

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