Which of the following best describes how chemical changes differ from physical changes?

• A. Chemical changes only affect the state of matter, while physical changes change the chemical composition.
• B. Chemical changes are always reversible, whereas physical changes are always irreversible.
• C. Chemical changes result in the formation of new substances with different chemical properties, while physical changes do not alter the chemical identity of a substance.
• D. Chemical changes do not involve energy changes, but physical changes always require energy.

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the definitions of physical and chemical changes. A physical change affects the form or state of a substance without changing its chemical composition, such as melting or boiling.
2. Step 2: Recognize that a chemical change results in the formation of one or more new substances with different chemical properties and compositions, such as rusting or burning.
3. Step 3: Analyze the options given by comparing them to these definitions. For example, physical changes do not change chemical identity, so any statement claiming they do is incorrect.
4. Step 4: Note that chemical changes often involve energy changes (either absorption or release), so the statement that chemical changes do not involve energy is false.
5. Step 5: Conclude that the best description is the one stating that chemical changes produce new substances with different chemical properties, while physical changes do not alter the chemical identity of the substance.