Generally, nanothermodynamics differs from the thermodynamics of small systems by the need to taking into account the size dependence of the surface tension of a nanoparticle. Attention is also given to the development of Gibbs' thermodynamics, namely, a more rigorous definition of the separating surface and a more general mechanical equilibrium condition are given. The dependence of the chemical potential of a substance in the bulk and surface layer of a nanoparticle the size of what - the nanoparticle or the substance is analyzed with emphasis on the surface tension effect. Stable and unstable equilibrium states during microphase growth are revealed.