This lecture introduces the fundamentals of chemical engineering, covering material balances, energy balances, reactive processes, and Hess's Law. Students will learn to apply Hess's Law to calculate heats of reaction and understand the principles behind it. Through examples, they will practice calculating heats of reaction using Hess's Law and learn about heats of combustion. The lecture concludes with a challenging problem on mass and energy balances in a reactive system with recycle. Students will gain practical skills in solving complex chemical engineering problems.