Thermodynamics is an integral and overarching discipline that is ubiquitous not only in engineering courses, but also courses beyond engineering (e.g., Physics, Material Science, and Chemistry). Thermodynamics studies the internal motions of bodies, and almost all substances encountered day-to-day are body systems of one form or another. Hence this topic is fundamental and can be widely applied. This chapter will deepen understanding of theoretical concepts through rigorous practice of challenging real-life problems, which include concepts on fugacity, nonideal behavior in gases and liquids, excess Gibbs energy and associated empirical models (e.g., Margules equations), and a variety of multiphase equilibrium problems. The step-by-step explanations and presentation of mathematical workings in the worked solutions will allow readers to easily follow the thought process in solving the problems presented.