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Unformatted text preview: hat some CO2 in the combustion chamber dissociated into CO and O2. Yet a third possibility would be to have no reactions among the three components at all, that is, for the system to be in chemical equilibrium. It appears that although we know the temperature, pressure, and composition (thus the state) of the system, we are unable to predict whether the system is in chemical equilibrium. In this chapter we develop the necessary tools to correct this. Assume that the CO, O2, and CO2 mixture mentioned above is in chemical equilibrium at the specified temperature and pressure. The chemical composition of this mixture does not change unless the temperature or the pressure of the mixture is changed. That is, a reacting mixture, in general, has different equilibrium compositions at different pressures and temperatures. Therefore, when developing a general criterion for chemical equilibrium, we consider a reacting system at a fixed temperature and pressure. Taking the positive direction of heat transfer to be to the system, the increase of entropy principle for a reacting or nonreacting system was expressed in Chapter 7 as
dS sys dQ T
(161) 100% reactants Equilibrium composition 100% products FIGURE 162 Equilibrium criteria for a chemical reaction that takes place adiabatically. REACTION CHAMBER Control...
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- Summer '08