What is a chemical change? Provide an example?

• A. A physical change where the composition remains the same.
• B. A change that produces one or more new substances; example: burning wood or rusting iron.
• C. A change in the state of matter that does not alter composition.
• D. A change that only alters the appearance.

Answer: (B)

A chemical change happens when bonds are broken and new substances with different properties are formed, so the original materials are transformed into something different. This contrasts with physical changes, where the material’s composition stays the same even if its shape, size, or state changes.

Burning wood is a classic example: wood reacts with oxygen in the air to produce new substances such as carbon dioxide, water vapor, and ash. The material you started with is no longer present as wood, and you can’t simply reverse it with a physical change. Rusting iron is another example, where iron reacts with oxygen to form iron oxide, a substance with properties different from the original iron.

Noting changes like color shifts, gas production, temperature change, or the appearance of a precipitate helps identify a chemical change, since these signals indicate new substances are formed.