How do fundamental theories in thermodynamics, kinetics, and transport phenomena intersect within chemical engineering? Expound on how these theories underpin reactor design, process variable decision$-$making, and optimization strategies for achieving desired product outcomes. Additionally, delve into the integration of macroscopic and molecular$-$level phenomena in analyzing and simulating chemical processes. What role do mathematical models and computational tools play in this integration, and how do they contribute to enhancing efficiency, sustainability, and safety in industrial applications? Consider the broader implications of these theoretical foundations in addressing contemporary challenges and advancing the field of chemical engineering.