This guide covers IGCSE Chemistry reversible reactions and equilibrium. You will revise reversible reactions (⇌; can go both ways), dynamic equilibrium (rates equal; concentrations constant; in closed system), Le Chatelier (effect of concentration, temperature, pressure on position of equilibrium), and Haber process (N2 + 3H2 ⇌ 2NH3) as example.

Key concepts to revise

• Reversible – Reaction can go forward and backward (e.g. N2 + 3H2 ⇌ 2NH3); use ⇌.
• Dynamic equilibrium – In closed system; forward and backward rates equal; concentrations of all species constant (but not necessarily equal).
• Le Chatelier – If you change concentration, temperature or pressure, equilibrium shifts to reduce that change. Increase concentration of reactant → shift to products. Increase temperature → shift to endothermic direction. Increase pressure (gases) → shift to side with fewer moles of gas.
• Haber process – N2 + 3H2 ⇌ 2NH3; high pressure (fewer moles on right); moderate temperature (compromise: rate vs yield); Fe catalyst; used to make ammonia (fertilizers).

Exam tips and command words

• State – What is meant by dynamic equilibrium (rates equal; concentrations constant; closed system).
• Describe – The effect of increasing concentration of a reactant (shift to products); increasing temperature for exothermic forward reaction (shift to reactants).
• Explain – Why high pressure is used in Haber process (4 mol → 2 mol; shift to right; more NH3).
• Predict – The direction of shift when concentration, temperature or pressure is changed (Le Chatelier).

Common mistakes

• Saying at equilibrium “reaction stops” (reaction continues both ways; rates are equal).
• Saying “equilibrium shifts to the left” without stating why (e.g. to reduce the increase in temperature if forward is exothermic).
• Not stating that equilibrium is only in a closed system (no matter in or out).

Revision checklist

• Define dynamic equilibrium (rates equal; concentrations constant; closed system).
• State the effect of increasing concentration of a reactant on position of equilibrium (shift to products).
• Explain the use of high pressure in Haber process (shift to right; more NH3).
• Predict the effect of increasing temperature on an exothermic forward reaction (shift to reactants).

Next steps

Book a free trial with an IGCSE Chemistry tutor to practise equilibrium and Le Chatelier questions, or explore Tutopiya’s learning portal for more revision resources.

Ready to Excel in Your Studies?

Get personalised help from Tutopiya's expert tutors. Whether it's IGCSE, IB, A-Levels, or any other curriculum — we match you with the perfect tutor and your first session is free.

Book Your Free Trial