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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 K_f (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/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

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

See also※

• Conjugate variables
• Dimensionless numbers
• Intensive and extensive properties
• Thermodynamic databases for pure substances
• Thermodynamic variable

References※