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. Triatomic gas: 6 degrees of freedom, C_v = 3R.Q = μ C_v Δ T = 0.3 × 3 × 8.31 × 15 = 112.185 J ≈ 112.2 J. Substituting values gives 112.2 J, which matches expected kinetic theory result, confirming mean free path λ = 1/(√2 n π d²), ideal gas law P V =