Which of the following are chemical changes?
W. The evaporation of water
X. Burning of wood Y. Dissolution of sugar Z. Souring of milk
Solution: Chemical changes alter the identity of the substance. A reaction always leads to a chemical change. Physical changes, on the other hand, do not change the identity of a substance. Phase changes such as going from solid to liquid are most common physical changes.
Which of the answer choices represent a reaction? That must be X burning of wood and Z souring of milk.