Chapter 19: The First Law of Thermodynamics

The First Law of Thermodynamics is presented as the mathematical relationship ΔU = Q - W, where internal energy change equals heat added minus work done by the system, emphasizing that internal energy is a state function independent of the path taken between states. Students explore various thermodynamic processes including adiabatic transformations where no heat exchange occurs, isochoric processes at constant volume, isobaric processes at constant pressure, and isothermal processes at constant temperature. The chapter examines the internal energy of ideal gases, demonstrating that it depends solely on temperature and introducing the relationship ΔU = nCᵥΔT for temperature changes. Heat capacities at constant volume and constant pressure are analyzed, revealing the fundamental relationship Cₚ = Cᵥ + R and the heat capacity ratio γ = Cₚ/Cᵥ, which differs for monatomic and diatomic gases. Adiabatic processes receive special attention with the derivation of key relationships such as TVᵞ⁻¹ = constant and pVᵞ = constant, along with work calculations for adiabatic expansion and compression. Throughout the chapter, pressure-volume diagrams serve as graphical tools for visualizing thermodynamic processes and calculating work as the area under curves, while cyclic processes demonstrate energy conservation principles where systems return to their initial state.