Just imagine that you need to move from Russia to Georgia. You can climb on foot through the Caucasus, search for passable paths for a long time,and it's not a fact that you will be able to walk. This is a reaction without a catalyst. Or you can dig a tunnel and drive back and forth by car. This is the same reaction in the presence of a catalyst. At the same time, the presence of a tunnel does not depend on whether one car has passed through it or a million. The catalyst does not change during the reaction.
Just imagine that you need to move from Russia to Georgia. You can climb on foot through the Caucasus, search for passable paths for a long time,and it's not a fact that you will be able to walk. This is a reaction without a catalyst. Or you can dig a tunnel and drive back and forth by car. This is the same reaction in the presence of a catalyst. At the same time, the presence of a tunnel does not depend on whether one car has passed through it or a million. The catalyst does not change during the reaction.