Tham khảo tài liệu 'understanding non-equilibrium thermodynamics - springer 2008 episode 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 18 1 Equilibrium Thermodynamics A Review The Basic Problem of Equilibrium Thermodynamics To maintain a system in an equilibrium state one needs the presence of constraints if some of them are removed the system will move towards a new equilibrium state. The basic problem is to determine the final equilibrium state when the initial equilibrium state and the nature of the constraints are specified. As illustration we have considered in Box the problem of thermo-diffusion. The system consists of two gases filling two containers separated by a rigid impermeable and adiabatic wall the whole system is isolated. If we now replace the original wall by a semi-permeable diathermal one there will be heat exchange coupled with a flow of matter between the two subsystems until a new state of equilibrium is reached the problem is the calculation of the state parameters in the final equilibrium state. Box Thermodiffusion Let us suppose that an isolated system consists of two separated containers I and II each of fixed volume and separated by an impermeable rigid and adiabatic wall see Fig. . Container I is filled with a gas A and container II with a mixture of two non-reacting gases A and B. Substitute now the original wall by a diathermal non-deformable but semi-permeable membrane permeable to substance A. The latter will diffuse through the membrane until the system comes to a new equilibrium of which we want to know the properties. The volumes of each container and the mass of substance B are fixed Vị constant Vii constant mB constant but the energies in both containers as well as the mass of substance A are free to change subject to the constraints UI Uii constant mA mA constant. In virtue of the second law the values of UI UII mA mA in the new equilibrium state are such as to maximize the entropy . dS 0 and from the additivity of the entropy in the two subsystems I 1 n 1 1 wn V 1 1 n .B Fig. Equilibrium conditions for thermodiffusion
