What happens:
* Atoms rearrange: The atoms within the original substance break apart and recombine in a new way. This rearrangement creates new molecules with different structures and bonding arrangements.
* New bonds form, old bonds break: During the rearrangement, chemical bonds between atoms are broken and new ones are formed. This process involves the exchange or sharing of electrons.
* Energy is either released or absorbed: Chemical changes often involve the release or absorption of energy. This energy can be in the form of heat (exothermic reaction), light (like in a firefly), or electricity.
* Properties change: The new substance formed will have different properties than the original, such as:
* Color: Think of iron rusting (brown) or burning wood (turning black).
* Smell: Burnt toast or rotten eggs are examples of chemical changes that create new, unpleasant smells.
* Melting point: The temperature at which a substance melts will likely be different.
* Reactivity: The ability of the substance to react with other substances may change.
Examples of chemical changes:
* Burning wood: Wood combines with oxygen, producing ash, smoke, and energy (heat and light).
* Baking a cake: Ingredients like flour, sugar, and eggs react and change into a cake with a new texture and taste.
* Rusting iron: Iron reacts with oxygen and water to form iron oxide (rust), a different compound.
Key distinction from physical changes:
* Physical changes: Only the appearance or state of matter changes, not its chemical composition. For example, ice melting (solid to liquid) or cutting a piece of paper (changing shape) are physical changes.
In summary, a chemical change involves the formation of a new substance with different properties due to a rearrangement of atoms and the breaking and forming of chemical bonds.
