Which of the following observations most reliably indicates that a chemical change has occurred rather than a physical change?

• A. Dissolving a solid in a liquid
• B. Formation of a new substance with different properties
• C. Change in size or shape
• D. Change in state, such as melting or boiling

Answer: (B)

Verified step by step guidance

1. Understand the difference between physical and chemical changes: Physical changes affect the form of a substance but not its chemical composition, while chemical changes result in the formation of one or more new substances with different properties.
2. Analyze each observation: Dissolving a solid in a liquid is usually a physical change because the substance's chemical identity remains the same, even though it is dispersed in the liquid.
3. Consider changes in size or shape: These are physical changes because they do not alter the chemical composition of the substance.
4. Evaluate changes in state, such as melting or boiling: These are physical changes where the substance changes phase but retains its chemical identity.
5. Identify the observation that indicates a chemical change: Formation of a new substance with different properties is a hallmark of a chemical change, as it shows that the original substances have undergone a chemical reaction to produce something new.