Ch. 16 Key Terms - Chemistry | OpenStax

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Key Terms

entropy (S): state function that is a measure of the matter and/or energy dispersal within a system, determined by the number of system microstates often described as a measure of the disorder of the system

Gibbs free energy change (G): thermodynamic property defined in terms of system enthalpy and entropy; all spontaneous processes involve a decrease in G

microstate (W): possible configuration or arrangement of matter and energy within a system

nonspontaneous process: process that requires continual input of energy from an external source

reversible process: process that takes place so slowly as to be capable of reversing direction in response to an infinitesimally small change in conditions; hypothetical construct that can only be approximated by real processes removed

second law of thermodynamics: entropy of the universe increases for a spontaneous process

spontaneous change: process that takes place without a continuous input of energy from an external source

standard entropy (S°): entropy for a substance at 1 bar pressure; tabulated values are usually determined at 298.15 K and denoted $S_{298}^{°}$

standard entropy change (ΔS°): change in entropy for a reaction calculated using the standard entropies, usually at room temperature and denoted $Δ S_{298}^{°}$

standard free energy change (ΔG°): change in free energy for a process occurring under standard conditions (1 bar pressure for gases, 1 M concentration for solutions)

standard free energy of formation $(Δ G_{f}^{°})$: change in free energy accompanying the formation of one mole of substance from its elements in their standard states

third law of thermodynamics: entropy of a perfect crystal at absolute zero (0 K) is zero

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Authors: Paul Flowers, William R. Robinson, PhD, Richard Langley, Klaus Theopold
Publisher/website: OpenStax
Book title: Chemistry
Publication date: Mar 11, 2015
Location: Houston, Texas
Book URL: https://openstax.org/books/chemistry/pages/1-introduction
Section URL: https://openstax.org/books/chemistry/pages/16-key-terms

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