A closed self-organising system is driven by the free energy that is initially present in the form of chemical energy. We assume that the system has the same pressure and the same temperature as the environment. The free energy can be written as a Kullback information
, (1)
where the distributions P0 and P denote the normalised distributions pi0 = Vci0/N and pi = Vci/N, respectively. The reference system P0 represent a system in reaction equilibrium, and the non-equilibrium of the present system, characterised by P, can be interpreted as the system being prepared with an abundancy of a fuel that may be used in the process of structure formation. In the case of an open system where chemical substances are allowed to pass the system border, the concentrations in the system may be kept off equilibrium so that free energy is available both for the built-up and the maintenance of the spatial patterns.