The program calculates and draws thermodynamic equilibrium concentrations of species in complex chemical systems. It handles homogeneous solutions, dissolution, precipitation, titrations with acids, bases, or other components. Adsorption on up to five different particulate surfaces can be modeled with the choice of the Constant Capacitance, Diffuse Layer (Generalized Two Layer), Basic Stern Layer, or Triple Layer model to consider surface charges. Corrections for ionic strength can be made and activities calculated. Kinetic reactions can be simulated with one rate determining process in a system of otherwise fast thermodynamic chemical equilibrium. Two-dimensional logarithmic diagrams, such as pe-pH, or generally pX vs. pY, can be calculated. A drawing option is implemented. A library with over 1750 thermodynamic stability constants allows quick access, comfortable creation of input matrices and hence easy use of the program. A second library contains more than 300 solubility products that can be introduced if solid phases are modeled. Both libraries can be altered and extended with new reactions and stability constants. Output data are formatted for .xls or for import in a graphic program.

ChemEQL is an extended and user-friendly version of the original program MICROQL by John Westall. It runs on MacOSX, Windows, Linux, and Solaris. (For older Mac-operating systems there exists a Pascal-version of ChemEQL V2.0). The program is currently in use in both teaching and research.