This textbook introduces the molecular side of physical chemistry. It offers students and practitioners a new approach to the subject by presenting numerous applications and solved problems that illustrate the concepts introduced for varied and complex technical situations. The book offers a balance between theory, tools, and practical applications. The text aims to be a practical manual for solving engineering problems in industries where processes depend on the chemical composition and physical properties of matter. The book is organized into three main topics: (I) the molecular structure of matter, (II) molecular models in thermodynamics, and (III) transport phenomena and mechanisms. Part I presents methods of analysis of the molecular behavior in a given system, while the following parts use these methods to study the equilibrium states of a material system and to analyze the processes that can take place when the system is in a state of non-equilibrium, in particular the transport phenomena. is designed for upper-level undergraduate and graduate courses in physical chemistry for engineers, applied physical chemistry, transport phenomena, colloidal chemistry, and transport/transfer processes. The book will also be a valuable reference guide for engineers, technicians, and scientists working in industry. • Offers modeling techniques and tools for solving exercises and practical cases; • Provides solutions and conclusions so students can follow results more closely; • Step-by-step problem solving enables students to understand how to approach complex issues.