{, class="wikitable" style="float: right;"
! Approximate values of ''kT'' at 298 K
! Units
, -
, ''kT'' = , , J
, -
, ''kT'' = , , pN⋅nm
, -
, ''kT'' = , , cal
, -
, ''kT'' = , ,
meV
In physics, an electronvolt (symbol eV, also written electron-volt and electron volt) is the measure of an amount of kinetic energy gained by a single electron accelerating from rest through an electric potential difference of one volt in vacu ...
, -
, ''kT'' = {{val, kT=-174 , , dBm/Hz
, -
! colspan=2, {{center, Related quantities (also at 298 K)
, -
, ''kT/hc'' ≈ {{val, 207 {{cite web , title=Google Unit Converter , url=https://www.google.ca/search?ei=VzDnW4mbLOfMjwS694DYCw&q=k*298Kelvin%2Fh%2Fc+in+cm%5E-1&oq=k*298Kelvin%2Fh%2Fc+in+cm%5E-1&gs_l=psy-ab.3...2293.2598.0.3103.2.2.0.0.0.0.125.214.1j1.2.0....0...1.1.64.psy-ab..0.0.0....0.gYQvcs3LZis , accessdate=10 November 2018 , , cm−1
, -
, ''kT''/''e'' = 25.7 , , mV
, -
, ''RT'' = ''kT'' ⋅ ''N''A = {{val, 2.479 , , kJ⋅mol−1
, -
, ''RT'' = 0.593 , , kcal⋅mol−1
, -
, ''h''/''kT'' = 0.16 , , ps
''kT'' (also written as ''k''B''T'') is the product of the
Boltzmann constant
The Boltzmann constant ( or ) is the proportionality factor that relates the average relative kinetic energy of particles in a gas with the thermodynamic temperature of the gas. It occurs in the definitions of the kelvin and the gas constant, ...
, ''k'' (or ''k''B), and the
temperature
Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer.
Thermometers are calibrated in various temperature scales that historically have relied o ...
, ''T''. This product is used in
physics
Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which r ...
as a
scale factor
In affine geometry, uniform scaling (or isotropic scaling) is a linear transformation that enlarges (increases) or shrinks (diminishes) objects by a '' scale factor'' that is the same in all directions. The result of uniform scaling is similar ...
for
energy
In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of heat a ...
values in
molecular
A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioche ...
-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 {{nowrap, ''E'' / ''kT'' (see
Arrhenius equation
In physical chemistry, the Arrhenius equation is a formula for the temperature dependence of reaction rates. The equation was proposed by Svante Arrhenius in 1889, based on the work of Dutch chemist Jacobus Henricus van 't Hoff who had noted in 18 ...
,
Boltzmann factor
Factor, a Latin word meaning "who/which acts", may refer to:
Commerce
* Factor (agent), a person who acts for, notably a mercantile and colonial agent
* Factor (Scotland), a person or firm managing a Scottish estate
* Factors of production, su ...
). For a system in equilibrium in
canonical ensemble
In statistical mechanics, a canonical ensemble is the statistical ensemble that represents the possible states of a mechanical system in thermal equilibrium with a heat bath at a fixed temperature. The system can exchange energy with the heat b ...
, the probability of the system being in state with energy ''E'' is proportional to {{nowrap, ''e''−Δ''E'' / ''kT''.{{Cite book , last=Atkins , first=Peter , title=Atkins' Physical Chemistry , publisher=OUP Oxford , year=2010 , isbn=978-0-19-954337-3 , edition=9th , pages=564–591 , language=EN
More fundamentally, ''kT'' is the amount of
heat
In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is al ...
required to increase the thermodynamic
entropy
Entropy is a scientific concept, as well as a measurable physical property, that is most commonly associated with a state of disorder, randomness, or uncertainty. The term and the concept are used in diverse fields, from classical thermodynam ...
of a system by ''k''.
In
physical chemistry
Physical chemistry is the study of macroscopic and microscopic phenomena in chemical systems in terms of the principles, practices, and concepts of physics such as motion, energy, force, time, thermodynamics, quantum chemistry, statistical mecha ...
, as kT often appears in the denominator of fractions (usually because of
Boltzmann distribution
In statistical mechanics and mathematics, a Boltzmann distribution (also called Gibbs distribution Translated by J.B. Sykes and M.J. Kearsley. See section 28) is a probability distribution or probability measure that gives the probability t ...
), sometimes '' β'' = 1/kT is used instead of ''kT'', turning {{nowrap, ''e''−Δ''E'' / ''kT'' into {{nowrap, ''e''−βΔ''E''.
RT
''RT'' is the product of the molar
gas constant
The molar gas constant (also known as the gas constant, universal gas constant, or ideal gas constant) is denoted by the symbol or . It is the molar equivalent to the Boltzmann constant, expressed in units of energy per temperature increment per ...
, ''R'', and the
temperature
Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer.
Thermometers are calibrated in various temperature scales that historically have relied o ...
, ''T''. This product is used in
physics
Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which r ...
and
chemistry
Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds made of atoms, molecules and ions ...
as a scaling factor for
energy
In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of heat a ...
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
The Avogadro constant, commonly denoted or , is the proportionality factor that relates the number of constituent particles (usually molecules, atoms or ions) in a sample with the amount of substance in that sample. It is an SI defining con ...
, ''N''A. Its
dimension
In physics and mathematics, the dimension of a Space (mathematics), mathematical space (or object) is informally defined as the minimum number of coordinates needed to specify any Point (geometry), point within it. Thus, a Line (geometry), lin ...
is energy or ML2T−2, expressed in SI units as joules (J):
:''kT'' = ''RT''/''N''A