This book is the second of the six-volume series, which provides an extensive coverage of Physical Chemistry. Each volume includes a large number of illustrative numericals and typical problems to highlight the principles involved. IUPAC recommendations and SI units have been adopted throughout. The present book describes Introduction and Mathematical Background, and First Law of Thermodynamics, Thermochemistry, Second Law of Thermodynamics, Equilibrium Criteria A and G Functions, Systems of Variable Composition and Thermodynamics of Chemical Reactions.