In chemical engineering, theoretical foundations underpin various aspects of process design, optimization, and safety. Concepts such as thermodynamics, fluid mechanics, heat and mass transfer, and reaction kinetics form the basis of understanding chemical processes. Thermodynamics elucidates energy and entropy changes during reactions and phase transitions, crucial for designing efficient processes. Fluid mechanics and heat transfer principles govern fluid behavior and heat exchange within equipment. Reaction kinetics guides reactor design and optimization by elucidating reaction rates and mechanisms. Understanding these theories enables chemical engineers to develop safe, efficient, and sustainable processes across diverse industries, from pharmaceuticals to petrochemicals.