# The Thermodynamics of Chromatography - The Distribution of Standard Energy Between Different Types of Molecular Interactions > The Concept of Complex Formation > Page 49

As already
discussed, the complex is considered to have zero vapor pressure and is
stationary in the column. Thus, there are now two parts of the denominator, (_{})
the free solute activity coefficient and (1-c) the fraction of free solute.

The
thermodynamic equilibrium constant (K_{1})
is contained in the function,

_{}

where (K_{EQ}) |
is the thermodynamic equilibrium constant, |

(a_{DA}) |
is the activity of the complex in the stationary phase, |

(a_{D}) |
is the activity of the solute in the stationary phase, |

(a_{A}) |
is the activity of the stationary phase, |

(g_{DA}) |
is the activity coefficient of the complex, |

(g_{D}) |
is the activity coefficient of the solute, |

and (g_{A}) |
is the activity coefficient of the stationary phase. |