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.

Question

Which is the mistake in her description?

The total mass remains the same in physical changes.
The arrangement of particles may change in physical changes.
Atoms remain bonded to each other in physical changes.
Energy changes may occur in physical changes.

Answer 1

The mistake in Julia's description is that "atoms remain bonded to each other in physical changes."

In a physical change, such as boiling, the water changes from liquid to gas (steam), but the chemical bonds between the hydrogen and oxygen atoms in the water molecule (H₂O) do not break. The molecules remain intact, and only their arrangement and state change. Julia's statement that "the oxygen and hydrogen separate" implies that the atoms themselves are no longer bonded during the boiling process, which is incorrect. The atoms are still bonded together as H₂O molecules, even when they transition into steam.