Question

Which of the following are examples of physical change?

- Dew forms on a blade of grass
- Hydrogen balloon explodes when contacted with a flame
- A halloween light stick glows after shaking
- None of these are physical changes
- Browning meat

Answer 1

The halloween light stick glowing and the browning of meat are not physical changes but chemical changes. Physical changes are those changes that do not alter the chemical composition of a substance, such as melting ice or boiling water.

Step-by-step explanation:

Both the halloween light stick glowing after shaking and the browning of meat are examples of chemical changes, not physical changes. In the case of the light stick, when you shake it, you initiate a chemical reaction that produces light—this is chemiluminescence, a process where chemical energy is converted into light energy, signaling a change in the substance's chemical composition. The browning of meat is also a chemical change, known as the Maillard reaction, where heat causes the proteins and sugars in the meat to react and form new compounds, thereby changing the chemical structure of the meat and giving it a different flavor and color.

Physical changes, on the other hand, are transformations that do not alter the chemical composition of a substance. Examples of physical changes include the melting of ice, the boiling of water, and the mixing of sand and water. In each of these processes, the substances involved retain their chemical identities despite changes in their physical state or form.