The most common states of matter on planet Earth (and in the kitchen) are solid, liquid, and gas.
Plasma, another state of matter where ionized gasses and their electrons act as a whole instead of a bunch of atoms, is the most common state of matter in the universe and forms the sun. This state of matter, however, is not common to us in everyday life. Similarly, the Bose-Einstein state of matter, which is a superfluid near absolute zero, has been created in a laboratory laboratories.
Solids, liquids, and gasses are plentiful in our kitchens, and kitchens make great teaching tools for children.
Solids have a definite shape and a definite volume.
A stick of butter is a solid. Shaped like a stick, it is solid and it keeps that shape. It has a definite volume of a half of a cup.
Liquids have a definite volume, but not a definite shape.
A cup of water will always have the volume of one cup, even if it is poured into a different container. Liquid takes the shape of whatever container it is in, so if you pour it on a plate, the liquid is flat, but if you pour it into a graduated cylinder, it is tall and skinny.
Gasses do not have a definite volume or a definite shape.
Gasses fill up the space of their container, whether that container is little or big, so the volume of gasses changes. Gases take the shape of their container, so they do not have a fixed shape.
What is it called when mass transitions from one state to another?
When a solid becomes a liquid, we say it has melted.
Microwave butter and a solid will become a liquid. Leave an ice cube on the counter and you will turn a solid into a liquid. Place granulated sugar in a cast-iron skillet and heat it up while constantly stirring and the sugar will melt. You can make peanut brittle by adding some peanut butter and peanuts to the mixture, pouring it out on wax paper, and breaking it into pieces after it cools.
When a liquid becomes a gas, it has evaporated, or you can say it has vaporized.
Boil water to get steam, which is evaporated water.
When a solid becomes a gas, we say it has sublimated.
Leave ice cubes in the freezer for a long time (months), and you should notice the ice cubes shrinking. This is because the part of the ice sublimated into the air in the freezer.
The reverse of sublimation (gas to a solid) is deposition, and I have not come up with a kitchen example.
When a gas becomes a liquid, it has gone through condensation.
Put ice cubes and water in a dry glass. Wait a little bit and feel the outside of the glass. Water molecules from the air will form water on the outside of the class. This is condensation.
When liquid becomes a solid, it freezes.
Put water or juice in an ice cube tray and insert it into the freezer. It will freeze.