Which of the following observations does NOT indicate that a chemical reaction has occurred?

• A. Change in state from solid to liquid due to melting
• B. Production of a gas
• C. Formation of a precipitate
• D. Change in color

Answer: (A)

Verified step by step guidance

1. Understand the difference between physical changes and chemical changes. A chemical reaction involves the making or breaking of chemical bonds, resulting in new substances, while a physical change affects the form or state of a substance without changing its chemical identity.
2. Analyze each observation to determine if it indicates a chemical change or a physical change:
3. Production of a gas usually indicates a chemical reaction because new gaseous substances are formed.
4. Formation of a precipitate (a solid formed from a solution) indicates a chemical reaction because new solid substances are created from dissolved ions.
5. Change in color often signals a chemical reaction because it can result from the formation of new substances with different properties.
6. Change in state from solid to liquid due to melting is a physical change because it only involves a change in the physical state, not the chemical composition of the substance.