Gas Laws & Kinetic Theory — A/L Physics

Ideal Gas A hypothetical gas whose molecules occupy negligible volume and have no intermolecular forces. Real gases approximate ideal behaviour at low pressure and high temperature. For A/L problems, treat all gases as ideal unless stated otherwise. Example: Air at room temperature and 1 atm behaves nearly ideally.

Boyle’s Law At constant temperature, the pressure of a fixed mass of gas is inversely proportional to its volume. Mathematically, P ∝ (1)/(V) or P_1V1 = P_2V2 . Intuition: Squeezing a syringe (decrease volume) increases pressure felt on the plunger.

Charles’s Law At constant pressure, the volume of a fixed mass of gas is directly proportional to its absolute temperature. V ∝ T (T in Kelvin). Example: A hot air balloon expands when heated; if pressure remains constant, volume increases.

Pressure Law (Gay-Lussac’s Law) At constant volume, the pressure of a fixed mass of gas is directly proportional to its absolute temperature. P ∝ T . Real-world: A sealed aerosol can left in a hot car may burst because pressure rises with temperature.