Signature of Hydrophobicity Its Temperature Dependence

To determine z p from experiments, you measure the concentration c.su of the solute in the water phase and the concentration c.vo of the solute in the oil phase, at cquilihrium. The ratio is the partition coefficient ATT) = Csn /cso, which can change with temperature T. Such measurements give Jp (T) = -kTInA(T). (This works only if A and B are approximately the same si/e and nearly spherical. Chapter 31 shows that a different form of Afj is needed if one species is a polymer and is much larger than the other.) 

You can express Afj°(T) in terms of its enthalpic and entropic components (see Equation (9.25)), 

Equations (30.4) to (30.6) lead to a recipe for handling experimental data. 

However, when oils are dissolved in water, experiments show that ACp, 0. If ACp is independent of temperature. Equations (30.5) and (30.6) become 

Here s a convenient way to determine the quantities in Equation (30.9). Find the temperature Th at which the enthalpy is zero (you can show that Ah = 0 occurs where Ap°/IcT has a maximum or minimum). Also find the temperature Ts at which the entropy is zero (A5° = 0 where has a maximum or minimum). Then find the value of ACp that causes Equation (30.9), 

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