1. CATALYST - a substance that speeds up a chemical reaction but doesn't appear in the chemical equation because it is not permanently changed or used up.
2. INHIBITOR - a substance that slows down a chemical reaction.
3. ENDOTHERMIC REACTION - a reaction in which energy is absorbed.
4. EXOTHERMIC REACTION - A reaction in which energy is released.
5. ISOTOPES - atoms of the same element that have different numbers of neutrons.