Standard Article

Geochemical Modeling—Computer Code Concepts

Ground Water Hydrology

  1. Geoffrey Thyne

Published Online: 15 JUL 2005

DOI: 10.1002/047147844X.gw2460

Water Encyclopedia

Water Encyclopedia

How to Cite

Thyne, G. 2005. Geochemical Modeling—Computer Code Concepts. Water Encyclopedia. 5:142–145.

Author Information

  1. Colorado School of Mines, Golden, Colorado

Publication History

  1. Published Online: 15 JUL 2005


The formalism that allows us to relate mass actions equations (balanced chemical reactions) to actual solutions is called chemical thermodynamics or, more precisely, equilibrium thermodynamics. The basic idea is that elements, molecules, and compounds all contain some internal energy and that all systems try to reach a state where that energy is minimized (equilibrium). Natural systems, particularly low-temperature systems, do not always reach equilibrium, but they do move in that direction. The internal energy of an element, molecule, or compound is expressed as its enthalpy or internal heat. The free energy of an element is an element, molecule or compound is the sum of its internal heat and its internal tendency toward disorder (entropy).


  • geochemical models;
  • thermodynamic equilibrium;
  • kinetic;
  • formulations;
  • electrical balance;
  • equilibrium;
  • entropy;
  • water chemistry;
  • total free energy;
  • computer models