Video narration
When wet clothes dry, has a chemical reaction happened-or has water simply evaporated? Usually, the clothes are still the same material; water has just left their surface. A dehydration reaction is different: H2O is removed during a chemical change, from one molecule or from reacting molecules. The idea flips when water is part of the molecule arrangement. Take ethanol. When heated with an acid catalyst, ethanol can lose H2O and become ethene: C2H5OH → C2H4 + H2O. The atoms have been rearranged, so the product is a new substance with different properties. That is not the same as boiling water away from a liquid, or drying something that remains chemically unchanged. So, does dehydration just mean drying? No. In chemistry, it means removing H2O in a reaction, changing the molecular arrangement and producing a new substance-such as ethene from ethanol, instead.