How do chemical engineers apply theoretical principles to design, optimize, and operate processes in industries such as petrochemicals, pharmaceuticals, and materials manufacturing? Discuss the role of fundamental theories in thermodynamics, fluid mechanics, reaction kinetics, and transport phenomena. How do these theories underpin concepts like mass and energy balances, reactor design, separation processes, and process control? Explore the interplay between theoretical understanding and practical application, considering advancements like computational modeling, artificial intelligence, and sustainable process development. Finally, analyze the significance of theoretical frameworks in addressing contemporary challenges such as environmental sustainability, renewable energy integration, and resource efficiency in chemical engineering practice.