Which statement best describes a chemical change?

• A. A change that produces a new substance with different properties
• B. A change that alters the appearance but not the substance
• C. A change in which the substance changes state but remains the same substance
• D. A change that reverses itself when cooled

Answer: (A)

A chemical change is when bonds break and new bonds form to make a substance with properties different from the starting material. That change in chemical identity means you can often see evidence like a color change, gas bubbles, a precipitate, or heat being released or absorbed. In contrast, changing appearance without changing the substance (a physical change) or changing state (solid to liquid, liquid to gas) keeps the same substance, just in a different form. Reversing a change by cooling is typically a physical change as well, since you’re not creating a new substance. So the statement that describes a chemical change is the one that says a new substance with different properties is produced.