Equilibrium Constant
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Equilibrium constants of reactions involving gas mixtures
It is possible to work out the equilibrium constant for a chemical reaction involving a mixture of gases given the partial pressure of each gas and the overall reaction formula. For a reversible reaction involving gas reactants and gas products, such as:
aA + bB ↔ cD + dD
the equilibrium constant of the reaction would be:
KP = (PCc.PDd)/(PAa.PBb)
where:
KP = the equilibrium constant of the reaction
a = coefficient of reactant A
b = coefficient of reactant B
c = coefficient of product C
d = coefficient of product D
PCc = the partial pressure of C raised to the power of c
PDd = the partial pressure of D raised to the power of d
PAa = the partial pressure of A raised to the power of a
PBb = the partial pressure of B raised to the power of b
For reversible reactions, changes in the total pressure, temperature or reactant concentrations will shift the equilibrium so as to favor either the right or left side of the reaction in accordance with Le Chatelier's Principle. However, the reaction kinetics may either oppose or enhance the equilibrium shift. In some cases, the reaction kinetics may be the over-riding factor to consider.