Final answer:
Bubbles indicate both physical and chemical changes; boiling water causes bubbles in a physical change, while vinegar reacting with baking soda creates bubbles due to a chemical change that forms new substances.
Step-by-step explanation:
Bubbles forming in a substance can indicate both physical and chemical changes. To distinguish the two, let's consider examples:
- Physical change: When water boils, bubbles are formed due to the conversion of water from a liquid to a gaseous state (steam) at 100°C. This is a phase change, a typical physical process that does not alter the molecular structure of water (H2O remains H2O).
- Chemical change: Vinegar reacting with baking soda is a classic demonstration. Bubbles are observed due to the production of carbon dioxide gas (CO2) as a product of the chemical reaction between acetic acid in vinegar and sodium bicarbonate (baking soda). This reaction forms new substances, which characterizes a chemical change.
Therefore, while bubble formation can be an indicator of a chemical change, it's essential to consider the context and other signs, such as temperature changes, light emission, and unexpected color changes to correctly identify the type of change.