Effect of Operating Parameters on Equilibrium Conversion

The effeet of temperature on equilibrium eomposition ean be eal-eulated using the van t Hoff equation. Sinee the standard heat of reaetion is negative (-AH[ ) for an exothermie reaetion, an inerease in temperature results in a deerease in K and a subsequent deerease in eonversion. Therefore, an exothermie reaetion must be performed at as low a temperature as possible. An endothermie reaetion (+AH] ) is positive and K inereases with an inerease in temperature, as does the equilibrium eonversion. Therefore, an endothermie reaetion must be performed at an elevated temperature. 

The equilibrium eonstant K is independent of pressure with standard states. The effeet of the pressure is shown in Equation 6-6. K. is usually insensitive and may either inerease or deerease slightly with pressure. When (r -i- s) (a -i- b), the stoiehiometrie eoeffieients, an inerease in pressure P results in a deerease in eonversion of the reaetants to the produets (i.e., A -i- B o R -i- S). Alternatively, when (r -I- s) (a -I- b), an inerease in pressure P results in an inerease in the equilibrium eonversion. In ammonia synthesis (Nj -i- SHj o 2NH3), the reaetion results in a deerease in the number of moles. Therefore, an inerease in pressure eauses an inerease in equilibrium eonversion due to this faetor. 

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