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Liquids. Capillary effects

Problem 2.184

The surface of a soap film was increased isothermally by \(\Delta \sigma\) at a temperature \(T\). Knowing the surface tension of the soap water solution \(\alpha\) and the temperature coefficient \(d \alpha / d T,\) find the increment (a) of the entropy of the film's surface layer; (b) of the internal energy of the surface layer.

Reveal Answer
 (a) ΔS=−2(dα/dT)Δσ (b) ΔU=2(α−Tdα/dT)××Δσ.\text { (a) } \Delta S=-2(d \alpha / d T) \Delta \sigma \text { (b) } \Delta U=2(\alpha-T d \alpha / d T) \times \times \Delta \sigma .
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