In physics, a state of matter is one of the distinct forms that matter takes on. Four states of matter are observable in everyday life: solid, liquid, gas, and plasma.
It’s About the Physical"Phase" describes a physical state of matter. The key word to notice isphysical. Things only move from one phase to another by physical means. If energy is added (like increasing the temperature) or if energy is taken away (like freezing something), you have created a physical change.
When molecules move from one phase to another they are still the same substance. There is water vapor above a pot of boiling water. That vapor (or gas) can condense and become a drop of water in the cooler air. If you put that liquid drop in the freezer, it would become a solid piece of ice. No matter what physical state it was in, it was always water. It always had the same chemical properties.
On the other hand, a chemical change would build or break the chemicalbonds in the water molecules. If you added a carbon (C) atom, you would have formaldehyde (H2CO). If you added an oxygen (O) atom, you would create hydrogen peroxide (H2O2). Neither new compound is anything like the original water molecule. Generally, changes in the physical state do not lead to any chemical change in molecules.
Watch the video to review this concept.
States of Matter