For example, water has a critical temperature of 647 K (374 °C; 705 °F), which is the highest temperature at which liquid water can exist at any pressure. In theatmosphere at ordinary temperatures gaseous water (known aswater vapor) will condense into a liquid if itspartial pressure is increased sufficiently.
A vapor may co-exist with a liquid (or a solid). When this is true, the two phases will be in equilibrium, and the gas-partial pressure will be equal to the equilibriumvapor pressure of the liquid (or solid).[1]
The vapor-liquid critical point in a pressure-temperaturephase diagram is at the high-temperature extreme of the liquid–gas phase boundary (the dotted green line gives the anomalous behaviour of water).
Vapor refers to a gas phase at a temperature where the same substance can also exist in theliquid orsolid state, below thecritical temperature of the substance. (For example, water has a critical temperature of 374 °C (647 K), which is the highest temperature at which liquid water can exist.) If the vapor is in contact with a liquid or solid phase, the two phases will be in a state ofequilibrium. The termgas refers to a compressible fluid phase. Fixed gases are gases for which no liquid or solid can form at the temperature of the gas, such as air at typical ambient temperatures. A liquid or solid does not have to boil to release a vapor.
The constituentmolecules of a vapor possess vibrational, rotational, and translational motion. These motions are considered in thekinetic theory of gases.
Thevapor pressure is the equilibrium pressure from a liquid or a solid at a specific temperature. The equilibrium vapor pressure of a liquid or solid is not affected by the amount of contact with the liquid or solid interface.
For two-phase systems (e.g., two liquid phases), the vapor pressure of the individual phases are equal. In the absence of stronger inter-species attractions between like-like or like-unlike molecules, the vapor pressure followsRaoult's law, which states that thepartial pressure of each component is the product of the vapor pressure of the pure component and its mole fraction in the mixture. The total vapor pressure is the sum of the component partial pressures.[3]
Invisible water vapor condenses to form visible water droplets called mist
Perfumes contain chemicals that vaporize at different temperatures and at different rate in scent accords, known asnotes.
Atmosphericwater vapor is found near the earth's surface, and may condense into small liquid droplets and form meteorological phenomena, such asfog,mist, andhaar.
Flammable liquids do not burn when ignited.[4] It is the vapor cloud above the liquid that will burn if the vapor's concentration is between thelower flammable limit (LFL) and upper flammable limit (UFL), of the flammable liquid.
Since it is in the gas phase, the amount of vapor present is quantified by thepartial pressure of the gas. Also, vapors obey thebarometric formula in a gravitational field, just as conventional atmospheric gases do.
