In this book, an almost new approach to modern thermodynamics has been applied. One or more useful qualitative discussion statements have been extracted from each equation. These and other important statements were numbered and their titles were situated in an index entitled ""Helal and Others' statements, definitions and rules."" This ensures very quick obtaining of the required (for discussing and solving problems) statements, rules, definitions, equations, and their theoretical base that much eases reader's qualitative discussions and calculations. Almost all ideal gas closed system thermodynamic topics are either discussed in depth or deeply abbreviated. The topics discussed in depth are either new original ones or valuable classical ones that increase reader's ability for better understanding but are overlooked or deeply abbreviated in modern thermodynamic books. In both cases, they are significantly improved. The main five new ideas that are discussed in depth in this book are: (1) The ideal gas polytropic process for Cv = f(T) and its analysis (Chapter 6, Part I), (2) The theoretical realization of reversible gas state change processes ( 5-10), (3) Helal cycle (s 7-5-2), (4) Helal graphical method for comparing and discussing power cycles ( 7-5-4), and (5) the imperfection in the classical proof of Carnot's efficiency (theorem) and its exclusion (Chapter 7, final section). The deeply abbreviated topics are rigorously discussed in depth in the majority of modern thermodynamic books. To dissipate any misunderstanding, the equations and statements that can be misunderstood are followed by explanatory sentences (see equation 1-38 and the paragraph following it).