Which method is a reliable way to confirm that a chemical reaction has occurred?

• A. Noting a change in physical state, such as melting or boiling
• B. Detecting a change in color only
• C. Observing the formation of a new substance with different chemical properties
• D. Measuring a change in temperature alone

Answer: (C)

Verified step by step guidance

1. Understand that a chemical reaction involves the formation of new substances with different chemical properties, not just physical changes.
2. Recognize that changes in physical state (like melting or boiling) are physical changes, not chemical reactions, because the substance's chemical identity remains the same.
3. Note that a change in color alone may indicate a chemical reaction, but it is not always reliable because some physical changes can also cause color changes.
4. Consider that measuring a change in temperature alone is insufficient to confirm a chemical reaction, as physical processes can also release or absorb heat.
5. Conclude that the most reliable method to confirm a chemical reaction is to observe the formation of a new substance with different chemical properties, which indicates a true chemical change.