Catalysts: speeding up reactions
Chemistry · Key Stage 3 · The School
A catalyst is not used up
A CATALYST is a substance that speeds up a chemical reaction without being consumed in the process. It is not a reactant and does not appear as a product. It comes out at the end exactly as it went in, chemically unchanged, which means the same small amount of catalyst can keep working indefinitely.
How it actually speeds things up
A catalyst provides an alternative route for the reaction, one with a LOWER activation energy — a smaller hump for the reactants to get over. Lowering that hump means more reactant particles have enough energy to react at any given moment, so the reaction proceeds faster, without needing extra heat.
A biological catalyst: the enzyme
ENZYMES are catalysts made by living things, speeding up reactions inside cells that would otherwise be far too slow to sustain life. Digestion relies on enzymes to break down food quickly enough to be useful. The same principle as an industrial catalyst — speeding a reaction without being consumed — is at work inside your own body right now.
Hydrogen peroxide breaks down into water and oxygen on its own, but extremely slowly — barely any bubbles over several minutes. Add a small amount of manganese dioxide powder, and the same hydrogen peroxide fizzes rapidly, releasing oxygen fast enough to relight a glowing splint. Filter out the manganese dioxide afterwards, weigh it, and its mass is unchanged from before the reaction. It was never a reactant. It provided a faster route for the reaction and came out the other side exactly as it went in — which is the whole definition of a catalyst, demonstrated rather than just stated.