16.5: Key Terms
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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 | 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
second law of thermodynamics | all spontaneous processes involve an increase in the entropy of the universe
spontaneous change | process that takes place without a continuous input of energy from an external source
standard entropy (S°) | entropy for one mole of a substance at 1 bar pressure; tabulated values are usually determined at 298.15 K
standard entropy change (ΔS°) | change in entropy for a reaction calculated using the standard entropies
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 | 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