Thermodynamics key terms

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

• entropy (S)

• standard entropy (S°)

thermodynamic property defined in terms of system enthalpy and entropy; all spontaneous processes involve a decrease in G

• Gibbs free energy change (G)

• standard free energy change (ΔG°)

possible configuration or arrangement of matter and energy within a system

• spontaneous change

• microstate

process that requires continual input of energy from an external source

• reversible process

• nonspontaneous 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

• reversible process

• nonspontaneous process

all spontaneous processes involve an increase in the entropy of the universe

• second law of thermodynamics

• third law of thermodynamics

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

• standard entropy (S°)

• spontaneous change

entropy for one mole of a substance at 1 bar pressure; tabulated values are usually determined at 298.15 K

• standard entropy change (ΔS°)

• standard entropy (S°)

change in entropy for a reaction calculated using the standard entropies

• standard entropy change (ΔS°)

• standard entropy (S°)

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

• standard free energy change (ΔG°)

• Gibbs free energy change (G)