#
*kT* (energy)

* kT* (also written as

**) is the product of the Boltzmann constant,**

*k*_{B}*T**k*(or

*k*

_{B}), and the temperature,

*T*. This product is used in physics as a scale factor for energy values in molecular-scale systems (sometimes it is used as a unit of energy), as the rates and frequencies of many processes and phenomena depend not on their energy alone, but on the ratio of that energy and

*kT*, that is, on

*E*/

*kT*(see Arrhenius equation, Boltzmann factor). For a system in equilibrium in canonical ensemble, the probability of the system being in state with energy

*E*is proportional to

*e*

^{−ΔE / kT}.

Approximate values of kT at 298 K |
Units |
---|---|

kT = 4.11×10^{−21} | J |

kT = 4.114 | pN⋅nm |

kT = 9.83×10^{−22} | cal |

kT = 25.7 | meV |

kT/hc ≈ 207 [1] | cm^{−1} |

kT/e = 25.7 | mV |

RT = kT ⋅ N_{A} = 2.479 | kJ⋅mol^{−1} |

RT = 0.593 | kcal⋅mol^{−1} |

h/kT = 0.16 | ps |

More fundamentally, *kT* is the amount of heat required to increase the thermodynamic entropy of a system, in natural units, by one nat. *E* / *kT* therefore represents an amount of entropy per molecule, measured in natural units.

In macroscopic scale systems, with large numbers of molecules, *RT* value is commonly used; its SI units are joules per mole (J/mol): (*RT* = *kT* ⋅ *N*_{A}).

## RT

* RT* is the product of the molar gas constant,

*R*, and the temperature,

*T*. This product is used in physics as a scaling factor for energy values in macroscopic scale (sometimes it is used as a pseudo-unit of energy), as many processes and phenomena depend not on the energy alone, but on the ratio of energy and

**RT**, i.e.

*E/RT*. The SI units for

*RT*are joules per mole (J/mol).

It differs from *kT* only by a factor of the Avogadro constant, *N*_{A}. Its dimension is energy or ML^{2}T^{−2}, expressed in SI units as joules (J):

*kT*=*RT*/*N*_{A}

## References

- "Google Unit Converter". Google. Retrieved 10 November 2018.

- Atkins' Physical Chemistry, 9th ed., by P. Atkins and J. dePaula, Oxford University Press