Thermodynamic characteristics significant for supersaturated vapour condensation kinetics on soluble surfactant nuclei and observable at experiments were calculated using exact thermodynamic relations. The results calculated allow to analyze the effect of nucleus substance adsorption on a surface of formed drop depending on the external conditions. Frumkin adsorption isotherm accounting the lateral interactions in adsorbed monolayers of soluble surfactants is applied at calculations. The influence of lateral interactions on condensation activation energy is established under the conditions when almost all nucleus matter is absorbed on the drop surface.