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H1 Chemistry

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Chemical Equilibria

Explain a changing equilibrium, calculate its composition and connect the Haber process to rate and yield.

A-Level 8873, revised syllabus (2026-2027)

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3 topics

  1. Dynamic equilibrium

    Understand what stays constant and how a disturbance is opposed.

  2. Equilibrium quantities

    Construct Kc and calculate amounts without quadratic equations.

  3. Equilibrium in industry

    Explain the choices in an ammonia plant.

Scope and references

Learning outcomes and sources

8. Chemical Equilibria (8873, 2026 revision; examinations 2026 and 2027). Use the outcome map to find the explanation for a particular syllabus requirement.

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  1. 8(a) Explain reversible reactions and dynamic equilibrium.

    • Both directions occur; equal forward and reverse rates give constant concentrations in a closed system.

    Equilibrium is equal rates, not equal amounts

  2. 8(b) Apply Le Chatelier's Principle qualitatively.

    • State the principle; deduce concentration, pressure and temperature responses from supplied information.

    Predict the response to a disturbanceChoose a useful production rate and yield

  3. 8(c) Identify changes that affect the equilibrium constant.

    • Concentration, pressure and catalysts do not change Kc at fixed temperature; temperature does.

    Predict the response to a disturbanceKc describes an equilibrium ratioChoose a useful production rate and yield

  4. 8(d) Deduce concentration equilibrium expressions.

    • Correct species, coefficient powers and concentration units.

    Kc describes an equilibrium ratio

  5. 8(e) Calculate concentration equilibrium constants.

    • Use equilibrium data and stoichiometry where needed.

    Kc describes an equilibrium ratioUse the equation to link all the changes

  6. 8(f) Calculate equilibrium quantities.

    • Use supplied data; no solving of quadratic equations is required.

    Use the equation to link all the changes

  7. 8(g) Explain the Haber process conditions.

    • Industrial compromise: temperature, pressure, iron catalyst, separation and recycling.

    Choose a useful production rate and yield