Question

what is an example of a physical change?
○ having less ash than the paper that was burned to form it
○ ice forming and then melting back into water
○ rust having a different identity than the iron it forms on
○ the irreversible reaction of vinegar and baking soda

Explanation:

To determine an example of a physical change, we recall that physical changes do not alter the chemical identity of a substance, often involve phase changes (like melting/freezing) and are reversible.

• Burning paper (forming ash) is a chemical change (combustion, new substance).
• Rusting iron is a chemical change (new substance, rust).
• Vinegar + baking soda reaction is chemical (gas produced, new substances).
• Ice forming (freezing) and melting (liquefying) water: water (H₂O) remains H₂O, just changes state (phase change), reversible, so physical change.

Answer:

B. ice forming and then melting back into water