The First Law of Thermodynamics describes how energy flows into and out of systems through heat and work, and how these energy transfers affect a system's internal energy. In this chapter, ideal gases are used as model systems to explore thermodynamic pathways including isothermal, isobaric, isochoric, and adiabatic processes, leading to calculations of \(q\), \(w\), \(\Delta U\), and \(\Delta H\). Experimental techniques such as calorimetry are introduced as methods for measuring energy changes, while Hess' Law, standard enthalpies of formation, bond dissociation energies, and Born-Haber cycles provide tools for determining reaction enthalpies and understanding the energetics of chemical reactions.
Students should understand internal energy as a state function that measures a system's capacity to do work. They should be able to relate changes in internal energy to heat flow and work using the First Law of Thermodynamics.
Different thermodynamic pathways impose different constraints on the flow of heat and work. Students should be able to calculate \(q\), \(w\), \(\Delta U\), and \(\Delta H\) for ideal gases undergoing isothermal, isobaric, isochoric, and adiabatic processes.
Calorimetry provides an experimental method for measuring energy changes associated with physical and chemical processes. Students should be able to interpret calorimetric data and determine thermodynamic quantities from measured temperature changes.
Because enthalpy is a state function, reaction enthalpies can be determined by combining known thermochemical data. Students should be able to use Hess' Law and standard enthalpies of formation to calculate enthalpy changes for chemical reactions.
Bond dissociation energies provide a method for estimating reaction enthalpies when more precise thermochemical data are unavailable. Students should also be able to apply Hess' Law to thermodynamic cycles involving ionization energies, electron affinities, lattice energies, and Born-Haber cycles.