In chemical engineering, foundational theories underpin the design, analysis, and optimization of chemical processes across various industries. These encompass thermodynamics, governing energy transfer and chemical reactions; transport phenomena, analyzing momentum, heat, and mass transfer; reaction engineering, studying kinetics and reactor design; and process control, managing system dynamics and optimization. Additionally, materials science theories inform material selection and behavior in chemical processes. Environmental engineering theories address pollution prevention and sustainability. How do these theories collectively shape the modern practice of chemical engineering, and what challenges do they address in industries ranging from pharmaceuticals to petrochemicals and beyond?