This text presents physical chemistry as a coherent whole, rather than a set of disjointed topics, and shows how the subject relates to the rest of chemistry and physics. It emphasizes physical models as well as mathematical techniques, along with both rigorous and approximate (order-of-magnitude) problem-solving. Designed to progress beyond a numerical answer, problems expose the physical significance of the situation and teach students how to pose a problem in the first place. In addition, modern molecular concepts, currently unanswered problems in research, experimental techniques, and new directions in the field are introduced wherever appropriate. An orderly progression of thermodynamics carefully builds students' knowledge without covering too much too early on. Chemical reaction thermodynamics is covered in Chapter 7, after the culmination of thermodynamics, with advanced material in Chapter 10.