Liquid water vaporizes reversibly into steam at exactly () and external pressure: . Which of the fol — Thermodynamics and Thermochemistry Chemistry Question

💡 Solution & Explanation

(A) At the normal boiling point, liquid and vapor co-exist in thermodynamic equilibrium, so $\Delta G = 0$. (B) Gas possesses vastly more microstates and disorder than liquid, ensuring $\Delta S_{sys} > 0$. (C) Vaporization requires breaking hydrogen bonds, rendering it endothermic ($\Delta H > 0$). (D) $\Delta U = \Delta H - P\Delta V$. Since $\Delta H = 40.6 \text{ kJ/mol}$ and the expansion work term $P\Delta V \approx RT \approx 3.1 \text{ kJ/mol}$, $\Delta U$ remains strongly positive.