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A vapor (American spelling) or vapour (see spelling differences) is a substance in the gas
Gas

In physics, a gas is a state of matter, consisting of a collection of particles without a definite shape or volume that are in more or less random motion....
 phase at a temperature
Temperature

In physics, temperature is a physical property of a Physical system that underlies the common notions of hot and cold; something that feels hotter generally has the greater temperature....
 lower than its critical temperature
Critical temperature

The critical temperature, Tc, of a material is the temperature above which distinct liquid and gas phases of matter do not exist. As the critical temperature is approached, the properties of the gas and liquid phases become the same resulting in only one phase: the supercritical fluid....
. This means that the vapor can be condensed
Condensation

Condensation is the change of the physical state of aggregation of matter from gaseous phase into liquid phase. When the transition happens from the gaseous phase into the solid phase directly, bypassing the liquid phase the change is called Deposition , which is the opposite of sublimation....
 to a liquid
Liquid

Liquid is one of the principal states of matter. A liquid is a fluid that has the particles loose and can freely form a distinct surface at the boundaries of its bulk material....
 or to a solid
Solid

A solid object is in the states of matter characterized by resistance to deformation and changes of volume. In other words, it has high values both of Young's modulus and of shear modulus; this contrasts e.g....
 by increasing its pressure
Pressure

Pressure is the force per unit area applied to an object in a direction surface normal to the surface. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure....
, without reducing the temperature.

For example, water
Water

Water is a common chemical substance that is essential for the survival of all known forms of life. In typical usage, water refers only to its liquid form or States of matter, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam....
 has a critical temperature of 374°C (or 647 K) which is the highest temperature at which liquid water can exist.






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Watervapor Cup
A vapor (American spelling) or vapour (see spelling differences) is a substance in the gas
Gas

In physics, a gas is a state of matter, consisting of a collection of particles without a definite shape or volume that are in more or less random motion....
 phase at a temperature
Temperature

In physics, temperature is a physical property of a Physical system that underlies the common notions of hot and cold; something that feels hotter generally has the greater temperature....
 lower than its critical temperature
Critical temperature

The critical temperature, Tc, of a material is the temperature above which distinct liquid and gas phases of matter do not exist. As the critical temperature is approached, the properties of the gas and liquid phases become the same resulting in only one phase: the supercritical fluid....
. This means that the vapor can be condensed
Condensation

Condensation is the change of the physical state of aggregation of matter from gaseous phase into liquid phase. When the transition happens from the gaseous phase into the solid phase directly, bypassing the liquid phase the change is called Deposition , which is the opposite of sublimation....
 to a liquid
Liquid

Liquid is one of the principal states of matter. A liquid is a fluid that has the particles loose and can freely form a distinct surface at the boundaries of its bulk material....
 or to a solid
Solid

A solid object is in the states of matter characterized by resistance to deformation and changes of volume. In other words, it has high values both of Young's modulus and of shear modulus; this contrasts e.g....
 by increasing its pressure
Pressure

Pressure is the force per unit area applied to an object in a direction surface normal to the surface. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure....
, without reducing the temperature.

For example, water
Water

Water is a common chemical substance that is essential for the survival of all known forms of life. In typical usage, water refers only to its liquid form or States of matter, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam....
 has a critical temperature of 374°C (or 647 K) which is the highest temperature at which liquid water can exist. In the atmosphere
Earth's atmosphere

The Earth's atmosphere is a layer of gases surrounding the planet Earth that is retained by the Earth's gravity. Dry air contains roughly 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.038% Carbon dioxide in the Earth's atmosphere, and trace amounts of other gases....
 at ordinary temperatures, therefore, gaseous water is known as water vapor and will condense to liquid if its partial pressure
Partial pressure

In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. The total pressure of a gas mixture is the sum of the partial pressures of each individual gas in the mixture....
 is increased sufficiently.

A vapor may co-exist with a liquid (or solid). When this is true, the two phases will be in equilibrium, and the gas pressure will equal the equilibrium vapor pressure
Vapor pressure

Vapor pressure , is the pressure of a vapor in Thermodynamic equilibrium with its non-vapor Phase s. All liquids and solids have a tendency to evaporate to a gaseous form, and all gases have a tendency to Condensation back into their original form ....
 of the liquid (or solid).

Properties

Vapor refers to a gas phase at a temperature where the same substance can also exist in the liquid
Liquid

Liquid is one of the principal states of matter. A liquid is a fluid that has the particles loose and can freely form a distinct surface at the boundaries of its bulk material....
 or solid
Solid

A solid object is in the states of matter characterized by resistance to deformation and changes of volume. In other words, it has high values both of Young's modulus and of shear modulus; this contrasts e.g....
 state, below the critical temperature
Critical temperature

The critical temperature, Tc, of a material is the temperature above which distinct liquid and gas phases of matter do not exist. As the critical temperature is approached, the properties of the gas and liquid phases become the same resulting in only one phase: the supercritical fluid....
 of the substance. If the vapor is in contact with a liquid or solid phase, the two phases will be in a state of equilibrium
Thermodynamic equilibrium

In thermodynamics, a thermodynamics#Thermodynamic system is said to be in thermodynamic equilibrium when it is in thermal equilibrium, mechanical equilibrium, and chemical equilibrium....
. The term gas 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.

Vapor is responsible for the familiar processes of cloud
Cloud

A cloud is a visible mass of Drop or frozen crystals floating in the Celestial body atmosphere above the surface of the Earth or another planetary body....
 formation and condensation
Condensation

Condensation is the change of the physical state of aggregation of matter from gaseous phase into liquid phase. When the transition happens from the gaseous phase into the solid phase directly, bypassing the liquid phase the change is called Deposition , which is the opposite of sublimation....
. It is commonly employed to carry out the physical processes of distillation
Distillation

Distillation is a method of separation process mixtures based on differences in their Volatility in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....
 and headspace extraction
Headspace technology

Headspace technology is a technique to elucidate the odor compounds present in the air surrounding various objects Usually the objects of interest are odoriferous objects such as plants, flowers and foods....
 from a liquid sample prior to gas chromatography.

The constituent molecule
Molecule

In chemistry, a molecule is defined as a sufficiently stable, electric charge neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds....
s of a vapor possess vibrational, rotational, and translational motion. These motions are considered in the kinetic theory of gases.

Vapor pressure

The vapor pressure
Vapor pressure

Vapor pressure , is the pressure of a vapor in Thermodynamic equilibrium with its non-vapor Phase s. All liquids and solids have a tendency to evaporate to a gaseous form, and all gases have a tendency to Condensation back into their original form ....
 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.

The normal boiling point of a liquid is the temperature
Temperature

In physics, temperature is a physical property of a Physical system that underlies the common notions of hot and cold; something that feels hotter generally has the greater temperature....
 at which the vapor pressure
Vapor pressure

Vapor pressure , is the pressure of a vapor in Thermodynamic equilibrium with its non-vapor Phase s. All liquids and solids have a tendency to evaporate to a gaseous form, and all gases have a tendency to Condensation back into their original form ....
 is equal to one atmosphere (unit)
Atmosphere (unit)

The standard atmosphere is an international reference pressure defined as 101,325 Pascal and formerly used as unit of pressure . For practical purposes it has been replaced by the Bar which is 100,000 Pa....
.

For two-phase systems (e.g., two liquid phases), the vapor pressure of the system is the sum of the vapor pressures of the two liquids. In the absence of stronger inter-species attractions between like-like or like-unlike molecules, the vapor pressure follows Raoult's Law
Raoult's law

Established by Fran?ois-Marie Raoult, Raoult's law states:Once the components in the solution have reached chemical equilibrium, the total vapor pressure p of the solution is:...
, which states that the partial pressure
Partial pressure

In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. The total pressure of a gas mixture is the sum of the partial pressures of each individual gas in the mixture....
 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.

The physical chemistry
Physical chemistry

Physical chemistry is the application of physics to macroscopic, microscopic, atomic, subatomic, and particulate phenomena in chemical systems within the field of chemistry traditionally using the principles, practices and concepts of thermodynamics, quantum chemistry, statistical mechanics and kinetics....
 behind distillation
Distillation

Distillation is a method of separation process mixtures based on differences in their Volatility in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....
 is based on manipulating the equilibrium
Vapor-liquid equilibrium

Vapor-liquid equilibrium, abbreviated as VLE by some, is a condition where a liquid and its vapor are in Chemical equilibrium with each other, a condition or state where the rate of evaporation equals the rate of condensation on a molecular level such that there is no net vapor-liquid interconversion....
 occurring between the liquid and vapor phases of a molecule in solution
Solution

In chemistry, a solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is dissolved in another substance, known as a solvent....
.

Examples

  • Perfume
    Perfume

    Perfume is a mixture of fragrant essential oils and aroma compounds, fixatives, and solvents used to give the human body, animals, objects, and living spaces a pleasant smell....
    s contain chemicals that vaporize at different temperatures and at different rate in scent accords known as note
    Note (perfumery)

    Notes in perfumery are descriptors of scents that can be sensed upon the application of a perfume. Notes are separated into three classes; top notes, middle/heart notes, and base notes; which denote groups of smells that can be sensed with respect to the time after the application of a perfume....
    s.
  • Atmospheric
    Earth's atmosphere

    The Earth's atmosphere is a layer of gases surrounding the planet Earth that is retained by the Earth's gravity. Dry air contains roughly 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.038% Carbon dioxide in the Earth's atmosphere, and trace amounts of other gases....
     water vapor
    Water vapor

    Water vapor or water vapour , also aqueous vapor, is the gas phase of water . Water vapor is one Phase of the water cycle within the hydrosphere....
     is found near the earth's surface, and may condense into small liquid droplets and form meteorological phenomena such as fog
    Fog

    Fog is a cloud bank that is in contact with the ground. A cloud may be considered partly fog; for example, the part of a cloud that is suspended in the air above the ground is not considered fog, whereas the part of the cloud that comes in contact with higher ground is considered fog....
    , mist
    Mist

    Mist is a phenomenon of small droplets suspended in air. It can occur as part of natural weather or volcanic activity, and is common in cold air above warmer water, in Exhalationd air in the cold, and in a steam room of a sauna....
     and haar
    Haar (fog)

    In meteorology,Haar is a coastal fog along certain lands bordering the North Sea; the term is primarily applied in eastern Scotland. Research has shown that haar is typically formed over the sea and is brought to land by wind advection....
    .
  • Mercury-vapor lamp
    Mercury-vapor lamp

    A mercury-vapor lamp is a gas discharge lamp which uses Mercury in an excited state to produce light. The arc discharge is generally confined to a small fused quartz arc tube mounted within a larger borosilicate glass bulb....
    s and sodium vapor lamp
    Sodium vapor lamp

    A sodium vapor lamp is a gas discharge lamp which uses sodium in an excited state to produce light. There are two varieties of such lamps: low pressure and high pressure....
    s produce light from atoms in excited state
    Excited state

    Excitation is an elevation in energy level above an arbitrary baseline energy state. In physics there is a specific technical definition for energy level which is often associated with an atom being excited to an excited state....
    s.


Measuring vapor

Since it is in the gas phase, the amount of vapor present is quantified by the partial pressure
Partial pressure

In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. The total pressure of a gas mixture is the sum of the partial pressures of each individual gas in the mixture....
 of the gas. Also, vapors obey the barometric formula
Barometric formula

The barometric formula, sometimes called the exponential function Earth's atmosphere or isothermal atmosphere, is a formula used to model how the pressure of the air changes with altitude....
 in a gravitational field just as conventional atmospheric gases do.

Vapors of flammable liquids

Flammable liquid
Flammable liquid

File:Flammable liquid.gifGenerally, a Flammability liquid means a liquid which may catch fire easily.In the USA, there is a precise definition of flammable liquid as one with a flashpoint below 100 degrees Fahrenheit....
s do not burn when ignited. It is the vapor cloud above the liquid that will burn if the vapor's concentration is between the lower explosive limit and upper explosive limit of the flammable liquid.

See also

  • Evaporation
    Evaporation

    Evaporation is the slow vaporization of a liquid and the reverse of condensation. A type of phase transition, it is the process by which molecules in a liquid State of matter spontaneously become gaseous ....
  • Water vapor
    Water vapor

    Water vapor or water vapour , also aqueous vapor, is the gas phase of water . Water vapor is one Phase of the water cycle within the hydrosphere....
  • Dilution (equation)
    Dilution (equation)

    The dilution equation, also known as the Basic Room Purge Equation, is used in industrial hygiene. It determines the time required to reduce a known vapor concentration existing in a closed space to a lower vapor concentration....
  • Vapor pressure
    Vapor pressure

    Vapor pressure , is the pressure of a vapor in Thermodynamic equilibrium with its non-vapor Phase s. All liquids and solids have a tendency to evaporate to a gaseous form, and all gases have a tendency to Condensation back into their original form ....
  • Vapor Trail
  • Vaporizer
    Vaporizer

    A vaporizer is a device used to sublimate the active ingredients of plant material, commonly cannabis , tobacco, or any of many other therapeutic or medicinal herbs or blends ....
  • Gas phase
  • Henry's Law
    Henry's law

    In chemistry, Henry's law is one of the gas laws, formulated by William Henry in 1803. It states that:An equivalent way of stating the law is that the solubility of a gas in a liquid is proportional to the pressure of that gas above the liquid....
  • Raoult's Law
    Raoult's law

    Established by Fran?ois-Marie Raoult, Raoult's law states:Once the components in the solution have reached chemical equilibrium, the total vapor pressure p of the solution is:...