The Third Law of Thermodynamics postulates that the absolute entropy of a perfectly ordered crystall — Thermodynamics and Thermochemistry Chemistry Question

💡 Solution & Explanation

Residual entropy occurs when a molecule can adopt multiple energetically equivalent, or nearly equivalent, orientations in the crystal lattice at absolute zero, freezing into a disordered state. $CO$ (which can orient as CO or OC) and $N_2O$ (NNO or ONN) exhibit this. Ice also maintains residual entropy at 0 K due to orientational disorder in its hydrogen-bonded network (Pauling's ice rules). $CO_2$ is perfectly symmetric ($O=C=O$) and crystallizes unambiguously, strictly obeying the Third Law.