A catalyst is a substance that alters the rate of a chemical reaction while remaining chemically unchanged in mass and composition at the end.
A catalyst is a substance that alters the rate of a chemical reaction while itself remaining chemically unchanged in mass and composition at the end of the reaction. Malay: mangkin · Chinese: 催化剂.
A catalyst takes part in the reaction but is regenerated, so that after the reaction its mass and chemical nature are the same as before. A positive catalyst provides an alternative reaction path with a lower activation energy, so that a larger fraction of collisions is effective and the rate rises. A small amount of catalyst can speed up the reaction of a large amount of reactant, and the same catalyst can often be recovered and used again. A catalyst is usually specific, working for one reaction or a small group of reactions.
Example. Manganese(IV) oxide catalyses the decomposition of hydrogen peroxide into water and oxygen. Adding it makes the oxygen come off much faster, yet at the end the manganese(IV) oxide can be filtered off, dried and weighed, and its mass is unchanged. In industry, iron is used as a catalyst in the manufacture of ammonia.
Confusion to avoid. Do not confuse a catalyst with a reactant. A reactant is used up and its amount falls during the reaction; a catalyst is not used up and its mass is unchanged at the end. Also, a catalyst changes the rate and the activation energy, but it does not change the amount of product finally obtained or the overall energy change.
A catalyst is the practical pay-off of the collision theory: it works entirely by lowering the activation energy, so it links directly to the energy profile diagram and appears often in SPM Chemistry.
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