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
The total mass remains the same in physical changes.
B
The arrangement of particles may change in physical changes.
C
Atoms remain bonded to each other in physical changes.
D
Energy changes may occur in physical changes.
Explanation
Boiling is a physical change: water molecules move farther apart as the liquid becomes steam, but each molecule still contains two hydrogen atoms bonded to one oxygen atom. Separating the hydrogen and oxygen atoms would change the substance, so that part of Julia’s description is mistaken. The mass can remain the same, heat is involved, and cooling can turn steam back into liquid water.
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