Which of the following best describes how a physical change differs from a chemical change?

• A. A physical change does not alter the chemical composition of a substance, while a chemical change results in the formation of new substances.
• B. A physical change always produces energy, whereas a chemical change does not.
• C. A physical change cannot be reversed, but a chemical change can always be reversed.
• D. A physical change involves breaking chemical bonds, while a chemical change does not.

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the definitions of physical and chemical changes. A physical change affects the form or appearance of a substance but does not change its chemical identity, while a chemical change results in the formation of one or more new substances with different chemical compositions.
2. Step 2: Recognize that in a physical change, properties such as state (solid, liquid, gas), shape, or size may change, but the molecules themselves remain the same; no new substances are formed.
3. Step 3: In contrast, a chemical change involves breaking and forming chemical bonds, leading to new substances with different chemical properties and compositions.
4. Step 4: Evaluate the given options by comparing them to these definitions. For example, the statement that a physical change does not alter chemical composition aligns with the core concept of physical changes.
5. Step 5: Conclude that the best description is the one stating that a physical change does not alter the chemical composition of a substance, while a chemical change results in the formation of new substances.