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9476 / 2027
H2 Chemistry

Chemistry study notes

The Gaseous State

Know when the ideal-gas model works, calculate gas quantities and separate the pressures in a mixture.

A-Level 9476 (2026-2027)

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3 topics

  1. The ideal model and real gases

    Connect pressure to particle collisions and explain deviations.

  2. Use pV = nRT

    Choose consistent units and determine a molar mass.

  3. Partial pressures

    Use mole fractions and correct gas collected over water.

Scope

Learning outcomes

3. The Gaseous State. Use the outcome map to find the explanation for a particular syllabus requirement.

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  1. 3(a) State the ideal-gas kinetic-theory assumptions.

    • Negligible particle volume
    • No intermolecular forces
    • Random motion and elastic collisions
    • Mean kinetic energy and absolute temperature

    Pressure comes from collisions with the container

  2. 3(b) Explain when the ideal approximation succeeds or fails.

    • (i) Low pressure and high temperature
    • (ii) Very high pressure and very low temperature
    • Particle size and intermolecular forces

    Low pressure and high temperature favour ideal behaviour

  3. 3(c) Use pV = nRT, including relative molecular mass.

    • Consistent pressure, volume, temperature and R units
    • Amount, molar mass and density calculations
    • Distinguish molar mass from dimensionless Mr

    Convert the units before substituting

  4. 3(d) Use Dalton's law in gas mixtures.

    • Partial and total pressure
    • Mole fractions
    • Connection to gaseous equilibria

    Each gas contributes its own partial pressure