Difluoromethane

Difluoromethane

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Encyclopedia
Difluoromethane, also called HFC-32 or R-32, is an organic compound
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...

 of the dihalogenoalkane
Haloalkane
The haloalkanes are a group of chemical compounds derived from alkanes containing one or more halogens. They are a subset of the general class of halocarbons, although the distinction is not often made. Haloalkanes are widely used commercially and, consequently, are known under many chemical and...

 variety. It is based on methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...

, except that two of the four hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 atoms have been replaced by fluorine
Fluorine
Fluorine is the chemical element with atomic number 9, represented by the symbol F. It is the lightest element of the halogen column of the periodic table and has a single stable isotope, fluorine-19. At standard pressure and temperature, fluorine is a pale yellow gas composed of diatomic...

 atoms. Hence the formula is CH2F2 instead of CH4 for normal methane.

Physical properties

Property Value
Critical pressure (pc) 5.83 MPa
Critical temperature (Tc) 78.45 °C (351 K)
Compressibility factor
Compressibility factor
The compressibility factor , also known as the compression factor, is a useful thermodynamic property for modifying the ideal gas law to account for the real gas behavior. In general, deviation from ideal behavior becomes more significant the closer a gas is to a phase change, the lower the...

 (Z)
0.9863
Heat capacity at constant pressure (Cp) at 21 °C (70 °F) 0.043 kJ·mol−1·K−1
Heat capacity at constant volume (CV) at 21 °C (70 °F) 0.034 kJ·mol−1·K−1
Heat capacity ratio
Heat capacity ratio
The heat capacity ratio or adiabatic index or ratio of specific heats, is the ratio of the heat capacity at constant pressure to heat capacity at constant volume . It is sometimes also known as the isentropic expansion factor and is denoted by \gamma or \kappa . The latter symbol kappa is...

 (κ)
1.253

Uses


Difluoromethane is a refrigerant
Refrigerant
A refrigerant is a substance used in a heat cycle usually including, for enhanced efficiency, a reversible phase change from a liquid to a gas. Traditionally, fluorocarbons, especially chlorofluorocarbons, were used as refrigerants, but they are being phased out because of their ozone depletion...

 that has zero ozone depletion potential
Ozone depletion potential
The ozone depletion potential of a chemical compound is the relative amount of degradation to the ozone layer it can cause, with trichlorofluoromethane being fixed at an ODP of 1.0. Chlorodifluoromethane , for example, has an ODP of 0.055...

. Difluoromethane in a zeotropic (50%/50%) w/w mixture with pentafluoroethane
Pentafluoroethane
Pentafluoroethane is a refrigerant that has zero ozone depletion potential.It has the formula CF3CHF2. Although it has zero ozone depletion potential, it has high global warming potential, reported by the United States Environmental Protection Agency as 3450 times that of carbon...

 (R-125) is known as R-410A
R-410A
R-410A, sold under the trademarked names Puron, EcoFluor R410, Genetron R410A, and AZ-20, is a zeotropic, but near-azeotropic mixture of difluoromethane and pentafluoroethane , which is used as a refrigerant in air conditioning applications.-Environmental effects:Unlike many alkyl halide...

, a common replacement for various chlorofluorocarbons (aka Freon) in new refrigerant
Refrigerant
A refrigerant is a substance used in a heat cycle usually including, for enhanced efficiency, a reversible phase change from a liquid to a gas. Traditionally, fluorocarbons, especially chlorofluorocarbons, were used as refrigerants, but they are being phased out because of their ozone depletion...

 systems, especially for air-conditioning. The zeotropic
Zeotrope
A mixture of chemicals is said to be zeotropic if the composition of the vapor and the liquid phase at the vapor-liquid equilibrium state are never the same. Dew point and boiling point curve do not touch each other over the entire composition range with the exception of the pure components...

 mix of Difluoromethane with pentafluoroethane
Pentafluoroethane
Pentafluoroethane is a refrigerant that has zero ozone depletion potential.It has the formula CF3CHF2. Although it has zero ozone depletion potential, it has high global warming potential, reported by the United States Environmental Protection Agency as 3450 times that of carbon...

 (R-125) and tetrafluoroethane (R-134a) is known as R-407A
R-407A
R-407A is a mixture of gasses used as a refrigerant. It is a zeotropic blend of difluoromethane , pentafluoroethane and 1,1,1,2-tetrafluoroethane...

 through R-407E depending on the composition. Likewise the azeotropic
Azeotrope
An azeotrope is a mixture of two or more liquids in such a ratio that its composition cannot be changed by simple distillation. This occurs because, when an azeotrope is boiled, the resulting vapor has the same ratio of constituents as the original mixture....

 (48.2%/51.8% w/w) mixture with chlorotrifluoromethane
Chlorotrifluoromethane
Chlorotrifluoromethane, R-13, CFC-13, or Freon 13, is a non-flammable, non-corrosive chlorofluorocarbon and also a mixed halomethane. It is used as a refrigerant, however, due to concerns about its ozone-depleting potential, its use has been phased out due to the Montreal Protocol.-Physical...

 (R13). As a refrigerant difluoromethane is classified as A2L - slightly flammable [2009 ASHRAE Handbook]. Although it has zero ozone depletion potential, it has global warming potential
Global warming potential
Global-warming potential is a relative measure of how much heat a greenhouse gas traps in the atmosphere. It compares the amount of heat trapped by a certain mass of the gas in question to the amount of heat trapped by a similar mass of carbon dioxide. A GWP is calculated over a specific time...

675 times that of carbon dioxide, based on a 100-year time frame [May 2010 TEAP XXI/9 Task Force Report].

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