The Boltzmann Constant is the ratio of the Gas Constant R to Avogadro's number [[NA]]. It can be thought of as the gas constant for a single molecule (or even for an arbitrary particle in a colloidal solution) rather than for a mole.
The Boltzmann Constant is illustrated in the equation for the translational kinetic energy of a particle in thermal equilibrium with it's surroundings:
Where KEavg is the Kinetic Energy of the particle, k is the Boltzmann Constant, and T is the Temperature in Kelvin.
According to NIST the Boltzmann Constant has a value of 1.3806504 x 10-23 J/K with a standard uncertainty of 0.0000024 x 10-23 J/K and a relative uncertainty of 1.7 x 10-6 (this is represented by the concise form 1.380 6504(24) x 10-23 J/K
The Boltzmann Constant can also be represented in alternative units as 8.617385 x 10-5 eV/K/reference
- Fundamentals of Physics, Sixth Edition by David Halliday, Robert Resnick, and Jearl Walker p582