PV = nRT. Assumptions: (1) Gas molecules are point particles (negligible volume). (2) No intermolecular forces. (3) Elastic collisions (KE conserved). (4) Random motion in all directions. (5) Average KE proportional to T. Kinetic energy: KE = (3/2)kT per molecule = (3/2)RT per mole (k = R/N_A = Boltzmann constant = 1.38 x 10^-23 J/K). Pressure from kinetic theory: P = (1/3)(mN/V)u_rms^2 = (1/3)rho*u_rms^2. KE is independent of the nature of gas — depends only on temperature.