catalyst
A catalyst is a substance that makes a chemical reaction go faster — sometimes millions of times faster — yet comes out the other end completely unchanged, ready to do it all again. Think of it as a matchmaker at a party: it introduces two shy molecules, helps them pair up, then steps back untouched to introduce the next couple.
Every reaction has an energy hurdle to clear before it can happen, like a hill the reactants must climb. A catalyst doesn't shove them over the top — it quietly digs a lower, easier path around the hill, so far more molecules make it across each second. It speeds things up without ever being consumed.
Life runs on catalysts called enzymes — protein machines that carry out the chemistry of digestion, breathing, and growth at body temperature, work that would otherwise need blistering heat or take years. One common mix-up: a catalyst can't make an impossible reaction happen or change how much product you finally get. It only changes the speed, never the destination.
Hydrogen peroxide sits stable in its bottle for months, but add a speck of the enzyme catalase and it instantly fizzes into water and oxygen.
The enzyme speeds the breakdown enormously, yet is left intact to do it again.
The word was coined in the mid-1830s by Swedish chemist Jöns Jacob Berzelius, from the Greek katalysis, "a loosening or dissolving" — the sense that a catalyst loosens the bonds holding a reaction back. The everyday catalytic converter in a car's exhaust is a famous example, using platinum and other metals to scrub harmful gases into safer ones.