  The article presents new model of equilibrium in open chemical systems
suggesting a linear dependence of the reaction shift from equilibrium in
presence of the external thermodynamic force. Basic equation of this model
contains traditional logarithmic term and a non-traditional parabolic term. At
isolated equilibrium the non-traditional term equals to zero turning the whole
equation to the traditional form of constant equation. This term coincides with
the excessive thermodynamic function revealing linear relationship between
logarithm of the thermodynamic activity coefficient and reaction extent at open
equilibrium. Discovered relationship prompts us to use in many systems a
combination of the linearity coefficient and reaction shift from true
equilibrium rather then activity coefficients. The coefficient of linearity can
be found by thermodynamic computer simulation while the shift is an independent
variable defining the open equilibrium state. Numerical data obtained by
various simulation techniques proved premise of the method of chemical
dynamics.
