Pls help me define a catalyst.?
A substance which speeds up or slows down a reaction without taking part in it.
catalyst is a substance which increases or decreases the rate of recation without being involve in the reaction
A substance, usually used in small amounts relative to the reactants, that modifies and increases the rate of a reaction without being consumed in the process.
In chemistry and biology, catalysis is the acceleration (increase in rate) of a chemical reaction by means of a substance, called a catalyst, that is itself not consumed by the overall reaction. The word is derived from the Greek noun κατ?λυσι?, related to the verb καταλ?ειν, meaning to annul or to untie or to pick up. A catalyst provides an alternative route of reaction where the activation energy is lower than the original chemical reaction. Catalysts participate in reactions but are neither reactants nor products of the reaction they catalyze. An exception is the process of autocatalysis where the product of a reaction helps to accelerate the same reaction. They work by providing an alternative pathway for the reaction to occur, thus reducing the activation energy and increasing the reaction rate. More generally, one may at times call anything that accelerates a reaction, without itself being consumed or changed, a catalyst (for example, a catalyst for political change). A good example of a catalyst is in the disproportionation of hydrogen peroxide. Hydrogen peroxide reacts to give water and oxygen gas by itself: 2 H2O2 → 2 H2O + O2 Usually, this reaction is slow. On the addition of manganese dioxide to a dilute solution of hydrogen peroxide, an effervescence is observed, and much oxygen, detectable by a glowing splint, is evolved. The manganese dioxide may be recovered, and re-used indefinitely, thus it is a catalyst — it is not consumed by the reaction. A promoter is an accelerator of catalysis, but not a catalyst by itself. An inhibitor inhibits the working of a catalyst.
