Effects of a catalyst on a chemical equilibrium
"If an enzym is influencing an equilibrium, the value of the equilibrium constant K will change"
You know that a catalyst can influence the reaction rate of a chemical reaction.
Note: it can be a positive catalyst (increasing the reaction rate), but also a negative one (decreasing the rate).
In the case of a chemical equilibrium, two reaction are being influenced in the same way, with equal effect.
The forward reaction is equally in or decreased as the backward reaction.
What is the necessity to apply a catalyst if nothing changes by adding one?
The answer to that question has to do with the time needed to reach an equilibrium.
As longas the equilibrium still must be realised (and that may take a long time), such a catalyst can be very usefull, even necessary.
Chemical reactions can be very slow. A catalyst can shorten the period unto te, from hours, days may years, to maybe minutes or seconds.
Some equilibria will never be reached in practice without a catalyst.
In living creatures also are many catalysts: the bio-catalysts or: enzymes.
Most reactions in the metabolism are reactions in equilibrium. So it should be clear that enzymes will be supportive to reach the equilibria in time.
The human body has thousands of different enzymes, all very specific. Without those enzyme, no metabolism, and no life.