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?
ActivityaY
Chemical potentialμikJ/molYParticle number Ni
Compressibility (adiabatic)βS, κPa−1Y
Compressibility (isothermal)βT, κPa−1Y
Cryoscopic constantKfK·kg/molY
Densityρkg/m3Y
Ebullioscopic constantKbK·kg/molY
EnthalpyHJYY
Specific enthalpyhJ/kgY
EntropySJ/KYTemperature TY (entropic)
Specific entropysJ/(kg K)Y
FugacityfN/m2Y
Gibbs free energyGJYY
Specific Gibbs free energygJ/kgY
Gibbs free entropyΞJ/KYY (entropic)
Grand / Landau potentialΩJYY
Heat capacity (constant pressure)CpJ/KY
Specific heat capacity (constant pressure)cpJ/(kg·K)Y
Heat capacity (constant volume)CvJ/KY
Specific heat capacity (constant volume)cvJ/(kg·K)Y
Helmholtz free energyA, FJYY
Helmholtz free entropyΦJ/KYY (entropic)
Internal energyUJYY
Specific internal energyuJ/kgY
Internal pressureπTPaY
MassmkgY
Particle numberNiYChemical potential μi
PressurepPaYVolume V
TemperatureTKYEntropy S
Thermal conductivitykW/(m·K)Y
Thermal diffusivityαm2/sY
Thermal expansion (linear)αLK−1Y
Thermal expansion (area)αAK−1Y
Thermal expansion (volumetric)αVK−1Y
Vapor qualityχY
VolumeVm3YPressure P
Specific volumeνm3/kgY

See also