Does catalysts have any effect on the percentage yield for reactions?

Answer 1

In theory a catalyst has no effect on the yield. Like other posts said, the point of equilibrium will be reached sooner but it will be the same. However I do agree with the post which says that sometimes it is necessary to use a catalyst in order to "get" a reaction and otherwise the experimental yield could even be 0%. This doesn't mean that the reaction doesn't take place at all, but it occurs so slowly that within a reasonable time period the yield is very low sometimes close to zero.
So since we don't have the luxury to let the reaction take place on its own and wait even for decades, using the catalyst you reach the "end" of the reaction (point of equilibrium) within a good time frame.

Thus you could perform a reaction in the absence of a catalyst and get e.g. 50% yield and then do it in the presence of a catalyst and get 90%. It is not that the catalyst shifted the equilibrium, but it's just that the first reaction was not allowed to occur for enough time to reach the equilibrium. Only from this point of view can the catalyst increase the yield of our experiment.

or to rephrase it, a catlyst has no effect on the yield from a thermodynamic point of view but has one from the kinetic point of view. Since we allow the reaction to occur only for a certain time frame, the higher the reaction rate, the higher the yield.

Answer 2

I would disagree with the first two posters. A catalyst speeds up a reaction. Some reactions won't progress at all w/o a catalyst, so your reaction yield would be 0%. Some reactions take place only very slowly w/o catalyst, allowing for the formation of multiple side reactions, which increase impurities and decrease yield.

EDIT - OK, so a few here disagree w/ me. No prob. I understand the theoretical action of catalysts. BUT, practically speaking, any reaction that proceeds quickly to the product will be cleaner and higher yielding than one requiring forcing conditions because a catalyst was left out. The yield will be higher and the product more pure. I've spent that last 15 years in process development chemistry - w/ the goal of developing high yield and purity reactions for commercial production. I never once came across a reaction where the yield was the same or better w/o an optimized catalyst.

Answer 3

Sorry i disagree with the last poster. In any reaction which uses a catalysis, would take place without the catalysis, provided the required energy can be supplied. A catalyst has the effect of lowering the activation energy of the reaction. A catalysis is not used in a reaction, or does change the products or substrates, Therefore the reaction would still take place without the catalysis.

And on the question of percentage yield...A catalyst will increase the rate of the reaction, SO it will not even change the placing of an equilibrium, only speed up it takes to get there. I am guessing since you are talking about yields that an equilibrium is involved.

EDIT -Now i think people forget we are talking about percentage yeild and not yeild! The reaction rate has no effect on percentage yeild!

Answer 4

A catalyst is a substance which increases the rate at which a chemical reaction takes place. By their nature they catalyse any steps in the reaction which are reversible and therefore in no way affect the yield of the reaction. For example the formation of imines from ketones and amines will proceed slowly in the absence of acid but will eventually reach an equilibrium. If the imine is seperated out and left to stand in the same solvent the reaction will proceed to give some ketone and amine at the same equilibrium. Using a small quantity of acid decreases the time for the equilibrium to be reached in either the forward or reverse directions but not the position of the equilibrium.

Answer 5

If you are discussing reactions which reach a equilibrium then simply put - no. The catalyst speeds up both forward and backward reactions equally and has no effect on the equilibrium position and hence no effect on the yield.

Answer 6

A catalyst speeds up a reaction, it doesn't take part in the reaction itself. The yield won't be any more or less.

Definition: In chemistry, catalysis is the acceleration of a chemical reaction by means of a substance, called a catalyst, that is itself not consumed by the overall reaction

Gervald - tell me the reaction of the catalyst.

Answer 7

The above contributor is wrong in saying that a catalyst doesn't take part. Of course a catalyst takes part in a reaction, but it doesn't affect the total outcome - just how quickly you get there.

Answer 8

Not directly. But it may be able to make the system operate at a lower temperature (like in the Haber Process) thus increasing the yield