Final answer:
Option D, a cold pack being snapped causing the temperature to drop, represents a chemical change as new substances are formed through an endothermic reaction that absorbs heat.
Step-by-step explanation:
To determine which option is an example of a chemical change, it's important to differentiate between chemical and physical changes. A chemical change results in the formation of new chemicals with different molecular structures and properties, whereas a physical change only alters the appearance or state of a substance without changing its molecular structure.
- A scientist heating a copper penny until it melts (Option A) is an example of a physical change. The penny's composition remains the same: it simply changes from solid to liquid state.
- Mixing sugar and water to create lemonade (Option B) is another physical change because the sugar is merely dissolved in the water, and it can be recovered through evaporation.
- Water spilling on the ground and disappearing (Option C) is the physical change of evaporation; the water molecules remain unchanged as they transition from a liquid to a gas.
- A cold pack being snapped causing the temperature to drop (Option D) is the example of a chemical change. This is because when the cold pack is activated, chemicals inside react to create an endothermic reaction that absorbs heat, resulting in new substances.
Therefore, Option D is the correct answer: A cold pack is snapped, causing the temperature to suddenly drop is an example of a chemical change.