Chapter 2: First Law of Thermodynamics

First Law of Thermodynamics details the mathematical formulation of the First Law, illustrating how the change in a system's internal energy results from the difference between heat absorbed and work performed, while emphasizing the sign conventions for exothermic and endothermic interactions. A significant portion of the content is dedicated to defining enthalpy, a critical property for analyzing isobaric processes common in chemical reactions, and explaining its relationship to internal energy and the pressure-volume work term. The chapter systematically categorizes thermodynamic processes—isothermal, isochoric, isobaric, and adiabatic—and derives the specific relationships governing heat exchange and work for ideal gases under these conditions. Key concepts such as heat capacity are analyzed in depth, contrasting molar heat capacity at constant pressure against constant volume, and explaining the physical reasons why the former exceeds the latter. The summary also explores essential thermochemical principles, including Hess's Law, which establishes that enthalpy change is path-independent, and Kirchhoff's Law, which quantifies how the heat of reaction shifts with temperature changes based on the heat capacities of products and reactants. Finally, the text applies these theories to practical metallurgical scenarios, such as calcination, metallothermic reduction, and calculating latent heat during phase transformations like melting and vaporization.