Reference State solid solution

There is a large volume of contemporary literature dealing with the structure and chemical properties of species adsorbed at the solid-solution interface, making use of various spectroscopic and laser excitation techniques. Much of it is phenomenologically oriented and does not contribute in any clear way to the surface chemistry of the system included are many studies aimed at the eventual achievement of solar energy conversion. What follows here is a summary of a small fraction of this literature, consisting of references which are representative and which also yield some specific information about the adsorbed state. 

Oxidation states found only in solids are given in brackets numbers in bold indicate the most stable oxidation states in aqueous solution. Colours refer to aqueous solutions ... 

For a solution of a non-volatile substance (e.g. a solid) in a liquid the vapour pressure of the solute can be neglected. The reference state for such a substance is usually its very dilute solution—in the limiting case an infinitely dilute solution—which has identical properties with an ideal solution and is thus useful, especially for introducing activity coefficients (see Sections 1.1.4 and 1.3). The standard chemical potential of such a solute is defined as... 

Here /g,hq and y ,ss are the activity coefficients of component B in the liquid and solid solutions at infinite dilution with pure solid and liquid taken as reference states. A fus A" is the standard molar entropy of fusion of component A at its fusion temperature Tfus A and AfusGg is the standard molar Gibbs energy of fusion of component B with the same crystal structure as component A at the melting temperature of component A. 

The possibility of simulating the actual BWG ordering energy, rather than Cp, using a polynomial approximation was also examined by Inden (1976) using the disordered solid solution as a reference state. The following expression was suggested for a continuous second-order transformation such as A2/B2 ... 

The effect of intermolecular interactions can be readily observed when comparing the absorption spectrum of a molecule in solution to that in the solid state. In solution, where the molecules can be considered as isolated, the spectra are characterized by sharp lines corresponding to absorption bands. However, in the solid, intermolecular interactions cause the formation of exciton bands and splitting of the levels. This phenomenon is often referred to as Davydov splitting. This splitting is thus a measure of the strength of the interactions and for MOMs it can amount to 0.2-0.3 eV. 

We saw in Figure 1.2c that supramolecular chemistry is not just about solid state or solution host-guest chemistry but increasingly emphasises self-assembly and the construction of multi-nanometre scale devices and ultimately materials based on nanometre-scale components (a nanometre is 10 9 of a metre). Strict supramolecular self-assembly (Chapter 10) involves the spontaneous formation of a multi-component aggregate under thermodynamically controlled conditions based on information encoded within the individual building blocks (referred to as tectons ) themselves. The aggregate might comprise only one kind of molecule (as in the multiple copies of the same protein that comprise... 

Special consideration must be given to systems involving liquid solutions of at least one solid component, for which the choice of either the pure solid or pure supercooled liquid as the standard state is not convenient. This case is encountered for all solutions in which the pure solute is not chosen as the reference state. As an example, we consider an aqueous solution of a solid B and choose the reference state to be the infinitely dilute solution. Then a general change of state for the formation of the solution from the components is written as... 

When the reference state is the infinitely dilute solution, the standard state for the enthalpy is also the infinitely dilute solution. We then change the standard state of component B from the pure solid to the infinitely dilute solution by adding to and subtracting from Equation (9.30) the quantity n2H2, where H2 is the partial molar enthalpy of the component in the... 

Care must be taken to use or determine the correct change of state to which the change of entropy and enthalpy refers. The difficulty arises when one or more equilibrium reactions are present in addition to those used in determining the cell reaction. Such conditions occur when two or more phases are in equilibrium for example, the electrolytic solution may be saturated with a solid phase, or one of the electrodes may consist actually of a liquid solution that is saturated with a solid solution or with another liquid solution. Such equilibria do not alter the change of the Gibbs energy or the emf. Let the cell reaction be represented as v,Bj and an equilibrium reaction as... 

If specific enthalpies are unavailable, they can be estimated based on defined reference states for both solute and solvent. Often the most convenient reference states are crystalline solute and pure solvent at an arbitrarily chosen reference temperature. The reference temperature selected usually corresponds to that at which the heat of crystallization, AH c, of the solute is known. (The heat of crystallization is approximately equal to the negative of the heat of solution.) For example, if the heat of crystallization is known at Tref, then reasonable reference conditions would be the solute as a solid and the solvent as a liquid, both at Tref. The specific enthalpies could be estimated then as ... 

The doped semiconductor materials can often be considered as well-characterized, diluted solid solutions. Here, the solutes are referred to as point defects, for instance, oxygen vacancies in TiC - phase, denoted as Vq, or boron atoms in silicon, substituting Si at Si sites, Bj etc. See also -> defects in solids, -+ Kroger-Vink notation of defects. The atoms present at interstitial positions are also point defects. Under stable (or metastable) thermodynamic equilibrium in a diluted state, - chemical potentials of point defects can be defined as follows ... 

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