The enthalpy of dissolution of sodium decyl sulfate (SDeS) in water was mea
sured at 298 K in the region of true and micellar solutions (from 4.5 x 10(
-4) to 15 x 10(-2) mol/l) using an isoperibolic calorimeter. The dissolutio
n enthalpy isotherm has three maximums corresponding to the most essential
changes in the structure of the solutions: the full hydration boundary for
SDeS in true solutions, its first critical micellization concentration (CMC
1), and the intermediate micellar transition (CMC1-2). The energy of this t
ransition was estimated. Results obtained for the region of high dilutions
were discussed in terms of changes in the structure of the solvent in respo
nse to the introduction of Na+ and DeS(-) ions. Proposals regarding the ene
rgy and entropy contributions to the Gibbs energy of dissolution of SDeS in
water were made.