Justine observed that the water level in a dish placed on the window sill decreased after a few days, and vapor formed. What best explains that she observed a physical change?
Vapor can be easily condensed back to form water.
Water and its vapor react with substances in different ways.
The molecular composition of water changed when the water level decreased.
Bonds between hydrogen and oxygen broke when the water level changed.
Vapor can be easily condensed back to form water.
The best explanation for Justine's observation of a physical change is that water and its vapor react with substances in different ways.
The best explanation for Justine observing a physical change is that water and its vapor react with substances in different ways.
To understand why this is the case, we need to understand the properties of water and its vapor. Water (in its liquid state) and water vapor (in its gaseous state) are the same substance, H2O, but they exist in different physical states.
When water evaporates and turns into vapor, it undergoes a physical change, not a chemical change. In a physical change, the substance retains its molecular composition, but its physical state or properties can change. In this case, when water evaporates, it changes from a liquid state to a gaseous state, without any alteration to its molecular composition.
Justine observed a physical change because the water level decreased as the water evaporated and turned into water vapor. Water vapor is a gaseous state of water and has different physical properties compared to liquid water. It is not bonded together like liquid water, and the molecules are more spread out and move more freely. The change in physical state also resulted in the formation of vapor.
The other options, such as vapor condensation, change in molecular composition of water, or breaking of hydrogen-oxygen bonds, would be examples of chemical changes. However, in this case, the observation of the water level decreasing and vapor forming points more towards a physical change rather than a chemical change.