Gas Laws & Kinetic Theory — A/L Physics

What must I remember about Gas Laws & Kinetic Theory?

• Empirical Gas Laws: Boyle's Law: P1 V1 = P2 V2 (constant T); Charles's Law: V1 / T1 = V2 / T2 (constant P); Pressure (Gay-Lussac's) Law: P1 / T1 = P2 / T2 (constant V).
• Ideal Gas Equation of State: P V = n R T = N k_B T, where n is number of moles, R is universal gas constant (8.314 J·mol⁻¹·K⁻¹), N is total molecules, and k_B is Boltzmann constant (1.38 × 10⁻²³ J/K).
• Kinetic Theory Assumptions: Gas consists of identical, point-mass molecules in continuous random motion; perfectly elastic collisions; zero intermolecular forces except during negligible collision durations; total molecular volume is negligible compared to container volume.
• Kinetic Theory Pressure Equation: P = (1/3) ρ c_rms² = (1/3)(N m / V) c_rms²; Root-mean-square speed c_rms = √(3 k_B T / m) = √(3 R T / M).

Test yourself (1 minute)

1. Translational Kinetic Energy

   Average translational KE per molecule = (3/2) k_B T; depends SOLELY on absolute temperature T, independent of gas type or molecular mass.

2. Dalton's Law of Partial Pressures

   Total pressure exerted by a non-reacting mixture of gases equals the sum of partial pressures of individual components: P_total = P1 + P2 + ... + Pn.

3. Real Gas Deviation

   Real gases behave ideally only under LOW pressure and HIGH temperature (molecules far apart and moving fast, minimizing intermolecular attraction and finite volume effects).

Practise Gas Laws & Kinetic Theory questions today

Source: NIE G.C.E. (A/L) Physics Resource Book - Unit 4: Thermal Physics

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Where does Gas Laws & Kinetic Theory fit in the syllabus?

Unit 4.3 · Year 1 · Term 2