# The Thermodynamics of Chromatography - Thermodynamics Basics > Page 1

# Thermodynamics Basics

The retention
of a solute in a chromatographic system is determined firstly, by the magnitude
of the distribution coefficient of the solute between the two phases and
secondly, by the amount of stationary phase available to the solute for
interaction. This is fully discussed in Plate Theory
and Extensions of this series. In addition, the
*mechanism of distribution* has been considered exclusively on the basis
of molecular interactions in The Mechanism of Chromatographic Retention
. However, the distribution coefficient in
chromatography is an equilibrium constant and, consequently, it can be treated
rationally by conventional thermodynamics.

It follows, that
the distribution coefficient can be expressed in terms of the *standard
energy* of solute exchange between the phases employing the traditional and
well established Arrhenious relationship,

RT ln (K) = -DG^{o}
(1)

where (R) | is the gas constant, |

(T) | is the absolute temperature, |

and (DG^{o}) |
is the standard energy. |

Now, classical
thermodynamics gives another expression for the *standard
energy* which separates it into two parts, the *standard enthalpy *and the *standard entropy*.