Textbook in PDF format This book offers a balanced, modern introduction that is rigorous enough for engineering students yet intuitive and accessible for those in applied physics and related disciplines. Core topics such as irreversibility, non-quasistatic processes, and spontaneity, which are often treated vaguely or in non-intuitive ways, are developed here in a systematic, sequential manner. Concepts are introduced through simple examples and then expanded step-by-step, allowing the reader to build understanding gradually while still achieving conceptual rigor