Example of Chemical Equilibrium The Ammonia Synthesis

As an example of how these expressions are used in practical situations, we will calculate the extent to which the ammonia synthesis reaction 

In our calculation we assume that the gas mixture approaches equilibrium under conditions where the pressure is constant. This situation corresponds, for instance, to a volume of gas moving through a plug flow reactor with a negligible pressure drop. (Note that if the ammonia synthesis were carried out in a closed system, the pressure would decrease with increasing conversion.) 

By introducing the mole fraction Yx = PxIPtot where px is the partial pressure of gas X and p t is the total pressure, Eq. (22) can be formulated as  

This is a useful expression for calculating equilibrium concentrations. One can easily see that for an exothermic process (AH negative) the equilibrium concentration of products decreases with temperature, while it will also increase with pressure if the process consumes gas (vc + t A - )  

Using Eq. (32) for the ammonia synthesis and assuming ideal gas behavior, we immediately obtain 

---