Summarizing Phase Changes
Summary
- Most substances have three distinct phases: gas, liquid, and solid.
- Phase changes among the various phases of matter depend on temperature and pressure.
- The existence of the three phases with respect to pressure and temperature can be described in a phase diagram.
- Two phases coexist (i.e., they are in thermal equilibrium) at a set of pressures and temperatures. These are described as a line on a phase diagram.
- The three phases coexist at a single pressure and temperature. This is known as the triple point and is described by a single point on a phase diagram.
- A gas at a temperature below its boiling point is called a vapor.
- Vapor pressure is the pressure at which a gas coexists with its solid or liquid phase.
- Partial pressure is the pressure a gas would create if it existed alone.
- Dalton’s law states that the total pressure is the sum of the partial pressures of all of the gases present.
Glossary
PV diagram
a graph of pressure vs. volume
critical point
the temperature above which a liquid cannot exist
critical temperature
the temperature above which a liquid cannot exist
critical pressure
the minimum pressure needed for a liquid to exist at the critical temperature
vapor
a gas at a temperature below the boiling temperature
vapor pressure
the pressure at which a gas coexists with its solid or liquid phase
phase diagram
a graph of pressure vs. temperature of a particular substance, showing at which pressures and temperatures the three phases of the substance occur
triple point
the pressure and temperature at which a substance exists in equilibrium as a solid, liquid, and gas
sublimation
the phase change from solid to gas
partial pressure
the pressure a gas would create if it occupied the total volume of space available
Dalton’s law of partial pressures
the physical law that states that the total pressure of a gas is the sum of partial pressures of the component gases
This lesson is part of:
Temperature, Kinetic Theory, and Gas Laws