Degree symbol thermodynamic function

A degree symbol on a thermodynamic function, for example, ATT, indicates that the corresponding process has been carried out under standard conditions. The standard state for a substance is a precisely defined reference state. Because thermodynamic functions often depend on the concentrations (or pressures) of the substances involved, we must use a common reference state to properly compare the thermodynamic properties of two substances. This is especially important because, for most thermodynamic properties, we can measure only changes in the property. For example, we have no method for determining absolute values of enthalpy. We can measure enthalpy changes AH values) only by performing heat-flow experiments. 

A, the Helmholtz energy, is a thermodynamic potential for the canonical ensemble. Qnvt, often symbolized simply as Q, is the canonical partition function. The last of Eqs. (46) defines a fundamental equation in the Helmholtz energy representation by expressing as a function of N, V, T. Often in classical systems it is possible to separate the energy contributions that depend on the momenta only (kinetic energy K) from the potential energy V, which depends only on the coordinates. When Cartesian coordinates are used as degrees of freedom, for example, the partition function can be factorized as ... 

The task of finding a mathematical formulation of the second law of thermodynamics was accomplished by Sadi Carnot and Clausius on the traditional, macroscopic side, and, again, by Boltzmann from a molecular, statistical perspective. What is sought is a state function that quantitatively describes the degree of dispersion in a chemical system. This is entropy, and its symbol is S. It must increase in any irreversible process. 

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