Catalyst: definition in chemistry
Catalyst: A substance that speeds up a chemical reaction without being used up.
A catalyst provides a different reaction pathway with a lower activation energy, so more collisions between particles have enough energy to react. Because it is regenerated at the end, a small amount can be used again and again. Catalysts do not change which products form or the position of equilibrium, only how quickly it is reached, and enzymes are the catalysts of living things.
Examples
- Iron in the Haber process for making ammonia
- Platinum, palladium and rhodium in car catalytic converters
- Manganese dioxide (MnO₂) speeding up the breakdown of hydrogen peroxide
- Amylase, an enzyme in saliva that breaks down starch
On the periodic table
Many important catalysts are transition metals or their compounds, such as iron, nickel, platinum and vanadium(V) oxide, partly because these metals easily switch between oxidation states.