Learning Objectives
By the end of this section, you will be able to do the following:
- Interpret a phase diagram
- State Dalton’s law
- Identify and describe the triple point of a gas from its phase diagram
- Describe the state of equilibrium between a liquid and a gas, a liquid and a solid, and a gas and a solid
Up to now, we have considered the behavior of ideal gases. Real gases are like ideal gases at high temperatures. At lower temperatures, however, the interactions between the molecules and their volumes cannot be ignored. The molecules are very closecondensation occursand there is a dramatic decrease in volume, as seen in Figure 13.28. The substance changes from a gas to a liquid. When a liquid is cooled to even lower temperatures, it becomes a solid. The volume never reaches zero because of the finite volume of the molecules.
High pressure may also cause a gas to change phase to a liquid. Carbon dioxide, for example, is a gas at room temperature and atmospheric pressure, but becomes a liquid under sufficiently high pressure. If the pressure is reduced, the temperature drops and the liquid carbon dioxide solidifies into a snow-like substance at the temperature . Solid is called dry ice. Another example of a gas that can be in a liquid phase is liquid nitrogen . is made by liquefaction of atmospheric airthrough compression and cooling. It boils at 77 K at atmospheric pressure. is useful as a refrigerant and allows for the preservation of blood, sperm, and other biological materials. It is also used to reduce noise in electronic sensors and equipment, and to help cool down their current-carrying wires. In dermatology, is used to freeze and painlessly remove warts and other growths from the skin.