Chemically means in a way that involves chemistry or chemical reactions. When something happens chemically, atoms and molecules are rearranging themselves to create new substances with different properties.

When bread rises, yeast chemically converts sugar into carbon dioxide gas, creating those air bubbles that make bread fluffy. When iron rusts, it's combining chemically with oxygen in the air to form a completely new substance: that reddish-brown coating we call rust. Your body digests food chemically, breaking down complex molecules into simpler ones it can use for energy and growth.

Scientists use the word to describe how substances interact at the molecular level. Two clear liquids might look identical but behave very differently chemically. One might be water, the other vinegar. They have different chemical properties because their molecules are built differently.

The word helps us distinguish chemical changes from physical ones. Ice melting into water is a physical change, but wood burning into ash and smoke is a chemical change because new substances form. Understanding what happens chemically helps scientists create everything from medicines to batteries to better materials for building spacecraft.