PV = nRT
The ideal gas law PV = nRT combines Boyle's law (P∝1/V), Charles's law (V∝T), and Avogadro's law (V∝n) into a single equation. R is the universal gas constant: 0.08206 L·atm/(mol·K) or 8.314 J/(mol·K). At STP (0°C, 1 atm), 1 mole of any ideal gas occupies 22.414 L. The ideal gas law assumes: molecules have no volume, no intermolecular forces, and perfectly elastic collisions. Real gases deviate at high pressures and low temperatures — the van der Waals equation (P + a/V²)(V − b) = nRT corrects for this. Applications: calculating gas volumes in reactions, determining molar masses from gas density (M = dRT/P), atmospheric science, and engineering processes involving gases.