Phase Diagrams Effect of Pressure and Temperature on Physical State

Phase Diagrams Effect of Pressure and Temperature on Physical State 

The critical point. The liquid-gas line ends at the critical point. Picture a liquid in a closed container. As it is heated, it expands, so its density decreases. 

At the same time, more liquid vaporizes, so the density of the vapor increases. The liquid and vapor densities become closer and closer to each other until, at the critical temperature T ), the two densities are equal and the phase boundary disappears. The pressure at this temperature is the critical pressure (Pc). At this point, the average of the molecules is so high that the vapor cannot be condensed no matter what pressure is applied. 

The triple point of water occurs at low pressure (0.006 atm). Therefore, when solid water is heated at 1.0 atm, the horizontal dashed line crosses the solid-liquid line (at 0°C, the normal melting point) and enters the liquid region. Thus, at 

CHAPTER 12 Intermolecular Forces Liquids, Solids, and Phase Changes 

---