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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 and references

Learning outcomes and sources

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