Thermodynamics is a subject at the heart of chemistry as changes occur in many physical and chemical processes. This book tries to demystify the concepts on thermodynamics which is a core course in most undergraduate courses in majority of the universities in the world. The objective of the book is to survey practical and theoretical problems in both classical and modern thermodynamics. The emphasis is on the axiomatic approach to thermodynamics principles and the practical applications. To this end, the book tries to underpin the most abstract yet real aspects of thermodynamics. The book emphasizes problem solving and rigorous development of the underlying theories. The learner should call on other reference materials to fill some of the gaps that might be in the book. It should also be remembered that practice is essential to the learning process; the learner would do well to apply the techniques presented here by working many questions as provided in the extensive annotated self-test exercises. Another aspect of the book is the inclusion of reference materials to which the book was linked as provided in the references section.