Which statement best describes the difference between a physical change and a chemical change?

• A. Physical changes alter appearance or state without forming a new substance.
• B. Chemical changes form one or more new substances with different properties.
• C. Physical changes alter appearance or state without forming a new substance; chemical changes form one or more new substances with different properties.
• D. Chemical changes never involve a change in energy.

Answer: (C)

Physical changes affect how a material looks or what state it’s in, but the substance itself doesn’t become something new. Chemical changes, on the other hand, produce one or more new substances with different properties. That combination is captured here: physical changes alter appearance or state without forming a new substance, while chemical changes form new substances with different properties.

For example, ice melting to water is a physical change, because you still have H2O. Rust forming on iron is a chemical change, because you’ve produced a new substance with different properties. Energy can be involved in both kinds of changes, but a chemical change inherently results in new substances, which is what this statement emphasizes.