matter
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. , 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. Daltons law states that the total pressure is the sum of the partial pressures of all of the gases present.