12: Thermodynamics
Among the many capabilities of chemistry is its ability to predict if a process will occur under specified conditions. Thermodynamics, the study of relationships between the energy and work associated with chemical and physical processes, provides this predictive ability. Previous chapters in this text have described various applications of thermochemistry, an important aspect of thermodynamics concerned with the heat flow accompanying chemical reactions and phase transitions. This chapter will introduce additional thermodynamic concepts, including those that enable the prediction of any chemical or physical changes under a given set of conditions.
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- 12.2: The Second and Third Laws of Thermodynamics
- The second law of thermodynamics states spontaneous processes increases the entropy of the universe. If a process would decrease the entropy of the universe, then the process is nonspontaneous, and if no change occurs, the system is at equilibrium. The third law of thermodynamics establishes the zero for entropy at 0 J/Kelvin for a perfect, pure crystalline solid at 0 K with only one possible microstate.
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- 12.3: Free Energy
- Gibbs free energy (G) is a state function defined with regard to system quantities only and may be used to predict the spontaneity of a process. A negative value for ΔG indicates that the reaction will proceed in the forward direction to reach equilibrium; a positive ΔG indicates that the reaction will proceed in the reverse direction to reach equilibrium; and a ΔG of zero indicates that the system is at equilibrium. A number of approaches to the computation of free energy changes are possible.