Standard state

A defined reference condition used to express thermodynamic properties such as chemical potential and activity. Its precise convention depends on the substance and thermodynamic quantity.

Chemical potential: The change in a system’s Gibbs energy when its amount of a component increases at fixed temperature, pressure, and other component amounts. A component’s chemical potential is expressed relative to its standard chemical potential through its activity.
Thermodynamic system: A defined quantity of matter or region of space selected for thermodynamic analysis. A standard state is assigned to a substance within a specified thermodynamic framework.
Standard Gibbs energy of reaction: The Gibbs-energy change for a reaction when all reactants and products are in their specified standard states. It combines species’ standard chemical potentials into a reference reaction energy.
Standard temperature and pressure: A convention specifying reference values for temperature and pressure, with definitions varying among organizations and fields. Unlike a thermodynamic standard state, it usually specifies temperature and pressure together.
Activity (thermodynamics): A dimensionless effective concentration that accounts for nonideal interactions in a thermodynamic system. Activity equals one in the chosen standard state and measures departure from that reference.
Gibbs energy: A thermodynamic potential that predicts equilibrium and useful work at constant temperature and pressure. Standard-state Gibbs energies provide reference values for reactions and equilibrium calculations.
Equilibrium constant: A dimensionless quantity describing the composition of a system at chemical equilibrium for a specified reaction. Its thermodynamic definition uses activities relative to standard states.
Standard ambient temperature and pressure: A reference convention for ambient temperature and pressure used in some scientific and engineering contexts. It is a particular ambient-condition convention, not the general thermodynamic reference for activities.
Standard chemical potential: A substance’s chemical potential when its activity is one in a specified standard state. It is the reference value paired with activity in the chemical-potential equation.
Thermodynamic equilibrium: A state in which macroscopic properties are stable and no net thermodynamic driving forces remain. Standard states are reference conventions, not claims that a substance is actually at equilibrium.

Linked from 12 pages