Water is made of two hydrogen atoms and one oxygen atom bonded together. Julia is describing how water undergoes a physical change when it boils. She says that the particles shift to be farther apart and that the oxygen and hydrogen separate. She also says that the total mass of the steam is the same as the initial water, and that heat energy was required to cause the change. She finishes her description by saying that the steam can be turned back into water if it is cooled. Which is the mistake in her description?
Answer
A
Atoms remain bonded to each other in physical changes.
B
The total mass remains the same in physical changes.
C
Energy changes may occur in physical changes.
D
The arrangement of particles may change in physical changes.
Explanation
Boiling is a physical change: water molecules move farther apart as liquid water becomes steam, but each molecule remains H₂O. The hydrogen and oxygen atoms do not separate during boiling; breaking their bonds would be a chemical change. The other statements are consistent with a physical change: mass is conserved, heat is needed for boiling, and cooling can condense steam back into water.
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