Solid relative standard entropies

Relative Standard Entropies Gases, Liquids, and Solids As we saw in Section 17.3, the entropy... 

Relative Standard Entropies Allotropes As mentioned previously, some elements can exist in two or more forms—called allotropes— in the same state of matter. For example, the allotropes of carbon include diamond and graphite— both solid forms of carbon. Since the arrangement of atoms within these forms is different, their standard molar entropies are different ... 

Relative Standard Entropies Dissolution The dissolution of a crystalline solid into solution usually results in an increase in entropy. For example, consider the standard entropies of solid and aqueous potassium chlorate ... 

In contrast to AfG° and Afl° which are relative values (representing differences between values for the compound and the elemental reference states, arbitrarily assigned to be zero), standard entropy values, S° (Frame 16, section 16.2) are absolute values. This arises because the entropy of a perfectly crystalline solid at the absolute zero of temperature has a value of zero (Frames 16 and 17), i.e. ... 

In the previous section it was shown that the term heat of adsorption may represent different functions, depending on the experimental conditions under which it is determined. The situation is analogous with the entropy of adsorption which can also be defined in several ways (/1). It is always necessary to specify whether the function considered is a true differential, a derivative, or an integral entropy, and also whether it refers to an equilibrium state (defined by p and T) or to a standard state (defined by p° and T). Moreover, various entropies of adsorption may be defined by choosing different standard states for the adsorptive (this state may be gaseous, but also liquid or solid). In this section, all the thermodynamic quantities of the adsorbate will be defined relative to a Gibbs surface for simplicity, but defining them in terms of an interfacial layer yields the same results. 

The standard state of a substance is a reference state that allows us to obtain relative values of such thermodynamic quantities as free energy, activity, enthalpy, and entropy. All substances are assigned unit activity in their standard state. For gases, the standard state has the properties of an ideal gas, but at one atmosphere pressure. It is thus said to be a hypothetical state. For pure liquids and solvents, the standard states are real states and are the pure substances at a specified temperature and pressure. For solutes In dilute solution, the standard state is a hypothetical state that has the properties of an infinitely dilute solute, but at unit concentration (molarity, molality, or mole fraction). The standard state of a solid is a real state and is the pure solid in its most stable crystalline form. 

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