This book provides a sound foundation for understanding abstract concepts of phase and reaction equilibria (e.g. partial molar Gibbs energy, fugacity, and activity), and shows how to apply these concepts to solve practical problems using numerous clear examples. It also presents numerical methods necessary for solving real-world problems as well the basic mathematics needed, facilitating its use as a self-study reference work. In the example problems requiring MATHCAD^(R) for the solution, the results of the intermediate steps are given, enabling the reader to easily track mistakes and understand the order of magnitude of the various quantities involved.