ACTIVITIES IN CHEMICAL-REACTION RATE-EQUATIONS

The problem of the role of activities in chemical rate equations is an alyzed. The Mass Action Law - based formulation with concentrations an d the Thermokinetic chemical potential - based formulation are consist ent only in ideal systems. A new interpretation is presented for non-i deality using the concepts of ''fractions'': in a frame of three-level structure of physical chemistry. The fractions are the physico-chemic al components of the system between which only ideal relationships exi st. It is shown that activities really are concentrations of particula r fractions of the chemical components. In non-ideal mixtures the Mass Action Law is to be formulated with the fractions as participants in the elementary process instead of the chemical components. In this cas e the contradiction activity - concentration is dissolved.