Which of the following observations is always evidence of a chemical change?

• A. Dissolving sugar in water
• B. Change in temperature without any other change
• C. Formation of a new substance with different properties
• D. Change in the state from solid to liquid

Answer: (C)

Verified step by step guidance

1. Understand that a chemical change involves the formation of one or more new substances with different chemical properties and compositions compared to the original substances.
2. Analyze each observation to determine if it indicates a chemical change or a physical change:
3. Dissolving sugar in water is a physical change because the sugar molecules disperse but do not chemically alter; the substance remains sugar.
4. A change in temperature alone, without any other change, is not necessarily a chemical change; it could be a physical change such as heating or cooling.
5. A change in state from solid to liquid (melting) is a physical change because the substance's chemical identity remains the same.
6. Therefore, the observation that always indicates a chemical change is the formation of a new substance with different properties, as this means the original substances have undergone a chemical reaction.