The Boltzmann constant
(k or kB) is a
physical constant relating a gas's
mean particlekinetic energy to the gas's temperature.
For particles with no energy tied up in rotation or oscillation,
i.e., single atoms:
mean ke = (3/2)kT
mean ke - mean kinetic energy of particles in the gas.
T - temperature.
k - Boltzmann constant.
The Boltzmann constant is the gas constant
divided by the Avogadro constant.
Its value is 1.380649 × 10-16erg/K/mole.
It is key in statistical mechanics, the relating of statistical
properties of many individual particles to physical characteristics
we perceive at our own scale.
The Kelvin scale was re-standardized in 2017 such that this value
of the Boltzmann constant
is exact.
The new standard was considered reasonable because careful measures
of the Boltzmann constant under the previous Kelvin scale
standard were producing the same value repeatedly and reliably.