Practice question

**Internal energy of ideal gas** U = f/2 n R T depends only on temperature, f degrees of freedom, n moles, R=8.314 J/mol·K, for monatomic f=3 U=3/2 n R T, diatomic f=5 at moderate T U=5/2 n R T, independent of pressure or volume, only T matters for ideal gas. PV = μ R T, P = (μ R T)/(V).Total moles = 0.3 + 0.7 = 1.0, V = 20 × 10⁻³ m³.P = (1.0 × 8.31 × 350)/(20 × 10⁻³) = 1.45575 × 10⁵ Pa ≈ 1.46 atm. Substituting values gives 1.46 atm, which matches expected kinetic theory result, confirming mean free path λ