In thermodynamics, a physical property is any property that is measurable, and whose value describes a state of a physical system. Thermodynamic properties are defined as characteristic features of a system, capable of specifying the system's state. Some constants, such as the ideal gas constant, R, do not describe the state of a system, and so are not properties. On the other hand, some constants, such as Kf (the freezing point depression constant, or cryoscopic constant), depend on the identity of a substance, and so may be considered to describe the state of a system, and therefore may be considered physical properties.

"Specific" properties are expressed on a per mass basis. If the units were changed from per mass to, for example, per mole, the property would remain as it was (i.e., intensive or extensive).

Regarding work and heat

Work and heat are not thermodynamic properties, but rather process quantities: flows of energy across a system boundary. Systems do not contain work, but can perform work, and likewise, in formal thermodynamics, systems do not contain heat, but can transfer heat. Informally, however, a difference in the energy of a system that occurs solely because of a difference in its temperature is commonly called heat, and the energy that flows across a boundary as a result of a temperature difference is "heat".

Altitude (or elevation) is usually not a thermodynamic property. Altitude can help specify the location of a system, but that does not describe the state of the system. An exception would be if the effect of gravity need to be considered in order to describe a state, in which case altitude could indeed be a thermodynamic property.

Thermodynamic properties and their characteristics
PropertySymbolUnitsExtensive?Intensive?ConjugatePotential?
Activity a   Green tick
Chemical potential μi kJ/mol Green tick Particle
number Ni
Compressibility (adiabatic) βS, κ Pa−1 Green tick
Compressibility (isothermal) βT, κ Pa−1 Green tick
Cryoscopic constant[1] Kf K·kg/mol Green tick
Density ρ kg/m3 Green tick
Ebullioscopic constant Kb K·kg/mol Green tick
Enthalpy H J Green tick Green tick
    Specific enthalpy h J/kg Green tick
Entropy S J/K Green tick Temperature T Green tick (entropic)
    Specific entropy s J/(kg K) Green tick
Fugacity f N/m2 Green tick
Gibbs free energy G J Green tick Green tick
    Specific Gibbs free energy g J/kg Green tick
Gibbs free entropy Ξ J/K Green tick Green tick (entropic)
Grand / Landau potential Ω J Green tick Green tick
Heat capacity (constant pressure) Cp J/K Green tick
    Specific heat capacity
      (constant pressure)
cp J/(kg·K) Green tick
Heat capacity (constant volume) Cv J/K Green tick
    Specific heat capacity
      (constant volume)
cv J/(kg·K) Green tick
Helmholtz free energy A, F J Green tick Green tick
Helmholtz free entropy Φ J/K Green tick Green tick (entropic)
Internal energy U J Green tick Green tick
    Specific internal energy u J/kg Green tick
Internal pressure πT Pa Green tick
Mass m kg Green tick
Particle number Ni   Green tick Chemical
potential μi
Pressure p Pa Green tick Volume V
Temperature T K Green tick Entropy S
Thermal conductivity k W/(m·K) Green tick
Thermal diffusivity α m2/s Green tick
Thermal expansion (linear) αL K−1 Green tick
Thermal expansion (area) αA K−1 Green tick
Thermal expansion (volumetric) αV K−1 Green tick
Vapor quality[2] χ   Green tick
Volume V m3 Green tick Pressure P
    Specific volume ν m3/kg Green tick

See also

References

  1. Aylward, Gordon; Findlay, Tristan (2002), SI Chemical Data 5th ed. (5 ed.), Sweden: John Wiley & Sons, p. 202, ISBN 0-470-80044-5
  2. Cengel, Yunus A.; Boles, Michael A. (2002). Thermodynamics: an engineering approach. Boston: McGraw-Hill. p. 79. ISBN 0-07-121688-X.
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