CHEMICAL EQUILIBRIUM OF SIMPLE SYSTEMS IN THE IDEAL GAS STATE

Chemical equilibrium of simple systems in the ideal gas state... 

Chemical equilibrium of simple systems in the ideal gas state this relationship is shown in Fig. 10, for the system... 

There is no difficulty in calculating the chemical equilibrium of a system, in which a single chemical reaction takes place. The calculation, however, becomes increasingly difficult with the rising number of simultaneous reactions, until application of the same procedure to systems with more than three reactions proceeding simultaneously is practically impossible. Therefore, techniques have had to be worked out for more complicated chemically reacting systems, based on principles somewhat different from those of simple equilibrium calculation. The result are methods which allow equilibrium compositions to be calculated for systems of any degree of complexity whatever, in the ideal as well as real gas state. 

The total number of molecules does not change. As we have seen in section 3.7, the entropy of an ideal gas S(V,T,A) = A [5o +(V /iV) + CylnT]. Although there are considerable difference in the heat capacities of molecules with different numbers of atoms, the difference in the heat capacities of two diatomic molecules is relatively small. The difference in the term so is also small for two diatomic molecules. If we ignore these small differences in the entropy between the three species of diatomic molecule, then the entropy which depends on Nk, V and T will essentially remain constant if T and V are maintained constant. At the same time, since the number of molecules does not change, the pressure p remains constant (assuming ideal gas behavior). Since this reaction is exothermic, the removal of heat produced by the reaction is necessary to keep T constant. Under these conditions, both p and S remain constant as the reaction proceeds, and the enthalpy reaches its minimum possible value when the system reaches the state of equilibrium. For an arbitrary chemical reaction, Fand Thave to be simultaneously adjusted so as to keep p and S constant, which is not a simple task. 

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