Thermodynamics, like classical music, is an acquired taste. The initiation must be sensitively carried out, otherwise the mathematical rigour, like the formal structure of the music, acts to discourage a deeper relationship. It is sad but true that some students, both of thermodynamics and of Bach, never recover from the initial shock. In this, we are all losers. In this book, therefore, I have tried to pre- sent thermodynamics in a way which uses little mathematics, but which includes many practical and lively examples. I hope it will provide a basis for an intro- ductory course at Honours Degree level, and will also suffice for Higher National Diploma and Certificate students. In general, my aim has been to develop an understanding of Gibbs free energy fairly early on and then to apply this concept in several different fields. I have used many examples from chemical industry, in the firm belief that the basic usefulness of the subject must be demonstrated. I have therefore included a brief discussion of Ellingham diagrams in Chapter 10 and for a similar reason have omitted any mention of the Carnot cycle. I have used symbols consistent with the recommendations of the International Union of Pure and Applied Chemistry and have adopted units of the Systeme International d'Unites (SI).