Vant Hoff factor

One measure of the extent to which electrolytes dissociate is the vant Hoff factor, i. This factor is the ratio of the actual ue of a col-lig tive property to the value calculated when the substance is assumed to be a nonelectrolyte. Using the freezing-point depression, for example, we have... 

The amount of vapor-pressue lowering would also be affected by dissociation of an electrolyte. In calculating the mole fraction of solute and solvent, the number of moles of solute would have to be multiplied by the appropriate vant Hoff factor. 

Calculated vant Hoff factors are exact numbers [W Section 1.5],... 

Since the formation constants are easily accessible in chemistry, the standard vant Hoff isotherm transforms Eq. (80) into Eq. (81), whereby is often referred to as the Boltzmann factor of intermetallic interaction (Koper and Borkovec, 2001). 

Figure 6.6 shows the effect of temperature on the experimental efficiency of anthracene [5] and acetophenone [22] eluted with pure micellar solutions. The efficiency of acetophenone on a C18 column was multiplied by 12 when the temperature was raised from 25°C to 73°C [22]. A threefold enhancement was obtained for anthracene [5]. The retention factors were decreased by temperature. The magnitude of the k decrease is far less important than what was observed with alcohol additions [34]. The k decrease with temperature are predicted by the Vant Hoff equation (eq. 6.4). The equilibrium enthalpies and entropies of the retention process were measured in MLC for various surfactants [36]. These studies showed that the micellar retention process is essentially governed by entropic effects [3 6]. 

The factors F, were calculated from the Arrhenius or VanT Hoff equation ... 

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