anything that speeds up a reaction, chemical or otherwise, between two things
substance accelerate a chemical reaction
A substance which initiate the rate of chemical reaction without undergoing any change by itself till the end of the reaction.
OK- First about what a catalyst does. All reactions require some amount of energy to proceed. For most of of these it is not much and it comes from the reactions immediate environment and we don't notice it. This energy needed is called an energy threshold. Many, if not all, reactions can have their thresholds lowered by something else-platinum-nickle in the cars catalytic converter does this. Catalysts are not used in the reaction so the catalyst, once added, stays there and continues working. By the way, in biology we have organic catalysts (the enzymes).
catalyst is a substance that can cause a change in the rate of a chemical reaction without itself being consumed in the reaction; the changing of the reaction rate by use of a catalyst is called catalysis. Substances that increase the rate of reaction are called positive catalysts or, simply, catalysts, while substances that decrease the rate of reaction are called negative catalysts or inhibitors.
