Statistical Factors and Microscopic Constants

The observed, or macroscopic, equilibrium constant, K, of a generic chemical equilibrium (Eq. [34]) can be regarded as being given by the product of an intrinsic, or microscopic, equilibrium constant, K, and a statistical factor, 

The classical example is that of a symmetrical dicarboxylic acid. Since the two ends are chemically identical, the microscopic energy and therefore the microscopic equilibrium constant for the acid dissociation of each of the two groups is identical to, say, K. If we now look at the macroscopic level, we are not able to distinguish between the two ends of the molecules, and the observed, or macroscopic, first acid dissociation constant, is related to the probability that either site is deprotonated, thus Kai — 2. On the 

An accurate and consistent evaluation of statistical factors in self-assembly processes is of crucial importance to predict the expected stability constant in the absence of cooperative effects and, therefore, to spodight the emergence of either positive or negative cooperativity as a marked deviation firom statistical behaviour. However, the evaluation of statistical factors can be controversial and doubtful sometimes. A critical re-examination of the methods to assess statistical factors in self-assembly processes has been published in 2007. Two methods appear the most useful, namely, the symmetry number method and the direct counting method. The two methods if properly appHed give the same results however, the symmetry 

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