An ideal system, one component 
Uniform surface. We begin our discussion of the thermodynamic properties of small systems with the simplest case of adsorption of molecules of one kind (N is their number) distributed over sites of a uniform lattice with size M size in the absence of lateral interactions between molecules (s = 2). In this example, we will consider the basic problems of the analysis of small systems. To obtain expressions for the mean-square fluctuations, it is necessary to find the second derivative in the vicinity of the maximum of the distribution function lnP(N, M). Further, knowing the fluctuations of the distribution function, one can obtain the characteristics of interest taking into account the contribution of the fluctuations and determine their effect on the calculated characteristics (and on the observed experimental data).