Which process is characterized by the formation of new substances, such as rusting iron?

Which process is characterized by the formation of new substances, such as rusting iron?

• A. Physical Change
• B. Phase Change
• C. Nuclear Change
• D. Chemical Change

Answer: (D)

The formation of new substances signals a chemical change. In rusting, iron reacts with oxygen (and water) to form iron oxide, a compound with a different composition and properties than iron itself. This isn’t just a change in appearance or state; atoms are rearranged to make a new substance. Physical changes, by contrast, alter form or state without creating new chemicals—for example, ice melting to water. Phase changes involve changing state but not composition, and nuclear changes involve the nucleus and energy changes not present in rusting. So rusting is a chemical change because it produces a new substance.

The formation of new substances signals a chemical change. In rusting, iron reacts with oxygen (and water) to form iron oxide, a compound with a different composition and properties than iron itself. This isn’t just a change in appearance or state; atoms are rearranged to make a new substance. Physical changes, by contrast, alter form or state without creating new chemicals—for example, ice melting to water. Phase changes involve changing state but not composition, and nuclear changes involve the nucleus and energy changes not present in rusting. So rusting is a chemical change because it produces a new substance.