Standard thermodynamic functions ideal systems

In each case these parameters represent differences between the state function of the activated complex in a particular standard state and the state function of the reactants referred to in the same standard state. One is giving all the characteristics of a thermodynamic equilibrium constant, although it should be multiplied by a transitional partition function. For ideal systems the magnitude of AH° does not depend on the choice of standard state, and for most of the nonideal systems that are encountered the dependence is slight. For all systems, the magnitudes of AG° and AS0 depend strongly on the choice of standard state, so it is not useful to... 

As absolute values of free energies and potentials of substances are not known, we can only quote the differences between the values belonging to them in concrete cases and the values related to a certain, so called standard state. Values of other thermodynamic functions, such as internal energy, enthalpy, etc. are quoted in the same way. As the standard state of pure liquid or solid substances we consider their state in stable modification at 1 atm. pressure and at the temperature of the system. As the standard state for gas, either alono or in a mixture, the state of a pure gas in ideal state is taken at 1 atm. pressure and at the temperature of the system. 

The thermodynamic quantity 0y is a reduced standard-state chemical potential difference and is a function only of T, P, and the choice of standard state. The principal temperature dependence of the liquidus and solidus surfaces is contained in 0 j. The term is the ratio of the deviation from ideal-solution behavior in the liquid phase to that in the solid phase. This term is consistent with the notion that only the difference between the values of the Gibbs energy for the solid and liquid phases determines which equilibrium phases are present. Expressions for the limits of the quaternary phase diagram are easily obtained (e.g., for a ternary AJB C system, y = 1 and xD = 0 for a pseudobinary section, y = 1, xD = 0, and xc = 1/2 and for a binary AC system, x = y = xAC = 1 and xB = xD = 0). 

This equation is the link between tables of thermodynamic data (such as Table 4.2.1), which allow the evaluation of ArG°, and the equilibrium constant Kr of the reaction (sometimes also denoted as reaction quotient Qr), which is a function of the composition of the system in terms of concentration, molar fractions, and so on. The value and definition of Kr depends on the choice of the standard state and the ideality of the system, as shown subsequently for ideal and real gases, liquids, and gas-solid systems. 

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