The<unk>  (also known as the molar, universal, or ideal<unk> , usually denoted by symbol R) is a physical<unk>  which is featured in a large number of fundamental equations in the physical sciences, such as the ideal<unk>  law and the Nernst equation.  It is equivalent to the Boltzmann<unk> , but expressed in units of energy (i.e. the pressure-volume product) per kelvin per mole (rather than energy per kelvin per particle).
Its value is:
The two digits in parentheses are the uncertainty (standard deviation) in the last two digits of the value.
The<unk>  occurs in the simplest equation of state, the ideal<unk>  law, as follows:
where:
The<unk>  has the same units as specific entropy.
The Boltzmann<unk>  kB (often abbreviated k) may be used in place of the<unk>  by working in pure particle count, N, rather than number of moles, n, since
where 
N
A
{\displaystyle N_{A}}
 is Avogadro's number.
For example, the ideal<unk>  law in terms of Boltzmann's<unk>  is 
P
V
=
N
k
B
T
{\displaystyle PV=Nk_{B}T\,\!}
.
The specific<unk>  of a<unk>  or a mixture of<unk> es (
R
¯
{\displaystyle {\bar {R}}}
) is given by the universal<unk> , divided by the molar mass (
M
{\displaystyle M}
) of the<unk> /mixture.
It is common to represent the specific<unk>  by the symbol 
R
{\displaystyle R}
. In such cases the context and/or units of 
R
{\displaystyle R}
 should make it clear as to which<unk>  is being referred to. For example, the equation for the speed of sound is usually written in terms of the specific<unk> .
The specific<unk>  of dry air is
Gas constant
Fluency
Saturation 
Electrochemical gradient
Molecular mass
Chemical polarity
Density
Free energy