Kinetic Theory of Gases and Gas Laws

Nine connected videos that build the chapter layer by layer, in teaching order. Each part has a companion page with the key results, worked examples, common mistakes and practice questions. The formula sheet and the mixed practice set cover the whole chapter.

Learning path · Formula sheet · Practice set

Print and revise: Revision sheet (PDF) · Formula sheet (PDF, one page)

A transparent box of nitrogen molecules moving in random directions.

Part 1 of 9

Postulates of Kinetic Theory

State the ideal-gas model and explain why real gases approach it at high T and low P.

Basic postulates of an ideal gas · When real gases behave ideally

A cylinder of gas with a piston pushed down.

Part 2 of 9

Gas Laws

Use the ideal gas equation in all its forms, plus Boyle, Charles and Dalton, to solve state-change and mixture problems.

Boyle's law · Charles and Gay-Lussac's law · Ideal gas equation · Avogadro's number and hypothesis · Dalton's law of partial pressures

P–V isotherms with a liquid–vapour dome and the critical point C.

Part 3 of 9

Real Gases, Change of Phase and van der Waals Equation

Read real-gas P–V isotherms, define critical temperature, and apply the van der Waals corrections.

Real-gas isotherms and liquefaction · Critical point and critical temperature · van der Waals gas equation

A Torricelli barometer with a 76 cm mercury column.

Part 4 of 9

Pressure of Air and Barometric Relation

Explain the barometer and find how pressure varies with height or in rotating frames for an isothermal gas.

Torricellian barometer · Barometric relation

Two Maxwell–Boltzmann curves for nitrogen at 300 K and 1000 K.

Part 5 of 9

Distribution of Molecular Speeds

Interpret the Maxwell–Boltzmann distribution and compute rms, mean and most probable speeds.

Maxwell–Boltzmann distribution · Average velocity, rms, mean and most probable speed

A cube with one molecule; arrows show its momentum before and after hitting the wall.

Part 6 of 9

Pressure, Kinetic Energy and Temperature

Derive the kinetic-theory pressure formula and link molecular kinetic energy to absolute temperature.

Pressure exerted by a gas · Kinetic energy of gas molecules · Microscopic interpretation of temperature

Energy blocks for monatomic, diatomic and polyatomic molecules.

Part 7 of 9

Degrees of Freedom and Equipartition of Energy

Count degrees of freedom for different molecules and apply equipartition to find energy.

Translational degrees of freedom · Law of equipartition of energy · Monatomic, diatomic and polyatomic molecules

Energy blocks per mole for each type of molecule.

Part 8 of 9

Internal Energy of a Gas

Compute internal energy of single gases and mixtures, including mixing at constant volume.

Internal energy of an ideal gas · Equivalent degrees of freedom for a mixture · Mixing of gases at constant volume

A zigzag path through a box of molecules.

Part 9 of 9

Mean Free Path and Diffusion

Explain why gases spread slowly despite fast molecules, and use the mean free path and Fick's law.

Mean free path · Diffusion and Fick's law