6.3 Reversible Reactions and Equilibrium

2026 Syllabus Objectives

1. Core: State that some chemical reactions are reversible as shown by the symbol $\rightleftharpoons$
2. Core: Describe how changing the conditions can change the direction of a reversible reaction for: (a) the effect of heat on hydrated compounds (b) the addition of water to anhydrous compounds limited to copper(II) sulfate and cobalt(II) chloride
3. Supplement: State that a reversible reaction in a closed system is at equilibrium when: (a) the rate of the forward reaction is equal to the rate of the reverse reaction (b) the concentrations of reactants and products are no longer changing
4. Supplement: Predict and explain, for a reversible reaction, how the position of equilibrium is affected by: (a) changing temperature (b) changing pressure (c) changing concentration (d) using a catalyst using information provided
5. Supplement: State the symbol equation for the production of ammonia in the Haber process, $\mathrm{N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)}$
6. Supplement: State the sources of the hydrogen (methane) and nitrogen (air) in the Haber process
7. Supplement: State the typical conditions in the Haber process as 450°C, 20000 kPa / 200 atm and an iron catalyst
8. Supplement: State the symbol equation for the conversion of sulfur dioxide to sulfur trioxide in the Contact process, $\mathrm{2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)}$
9. Supplement: State the sources of the sulfur dioxide (burning sulfur or roasting sulfide ores) and oxygen (air) in the Contact process
10. Supplement: State the typical conditions for the conversion of sulfur dioxide to sulfur trioxide in the Contact process as 450°C, 200 kPa / 2 atm and a vanadium(V) oxide catalyst
11. Supplement: Explain, in terms of rate of reaction and position of equilibrium, why the typical conditions stated are used in the Haber process and in the Contact process, including safety considerations and economics