Shows that while the reaction proceed to catalyst coming participate in reactions with other substances as change for a while, but when the reaction ends, will revert back to the original substances.
Show that while the reaction proceeds catalyst will participate in reactions with other substances by changing a little while, but once the reaction has ended, will return to the original substance.
So while the reaction the catalyst will participate in the reaction with the change is another substance for a while, but when the reaction end return to original substance