Source: Extra Practice

Give two examples of changes from your daily life that are reversible and two that are irreversible. For each, briefly state why it falls into that category.

Model Answer

Two examples of reversible changes are:

  1. Melting of ice: Ice (solid water) changes to water (liquid) upon heating, and this water can be frozen back into ice by cooling. No new substance is formed.
  2. Stretching a rubber band: The rubber band changes shape when stretched but returns to its original shape when released. Its chemical composition remains the same. Two examples of irreversible changes are:
  3. Burning of a candle: The wax burns, producing new substances like carbon dioxide and soot, which cannot be converted back into wax.
  4. Cooking an egg: The proteins in the egg undergo a chemical transformation upon heating, forming new substances, and the cooked egg cannot revert to its raw state.

Explanation

Key points for grading:

  1. Two correct examples of reversible changes.
  2. Justification for each reversible change (no new substance, can revert).
  3. Two correct examples of irreversible changes.
  4. Justification for each irreversible change (new substance formed, cannot revert).