What foundational theories serve as the cornerstone for chemical engineering, shaping the understanding and practice of the discipline? How do principles of thermodynamics, kinetics, mass and energy balances, transport phenomena, and chemical kinetics interplay to form the theoretical framework guiding chemical engineers in designing processes and solving complex problems? Furthermore, how do these theories extend to diverse applications, from reactor design and optimization to separation processes and material synthesis? Exploring these theoretical underpinnings illuminates the essential tools and concepts empowering chemical engineers to innovate sustainable solutions, optimize industrial processes, and contribute to advancements across sectors from pharmaceuticals to renewable energy.