Heating and Cooling: States of Matter
What is matter? Matter is anything at all that takes up space and has mass -- "mass" is a measure of how much matter is in a given space. You already know that there are many different kinds of matter you can run into every day. But do you know the different kinds of matter and how heating and cooling relate to changing one kind of matter to another?
Solid matter is the most familiar kind; almost everything you interact with in a day is solid matter, including yourself! Solid matter is fixed into a rigid shape based on the bonds between particles. These invisible particles move around fixed positions that cannot be broken without adding or removing more energy. The volume of any solid object is also fixed -- "volume" is a measure of how much space matter takes up.
Liquid takes the shape of its container, so it can't ever be said to have a "rigid" shape. It has definite volume, so no matter what container you place it in, it will always fill up the same amount of space (naturally, though, transferring liquid from one container to the next is a good way to lose some of it and reduce the volume!) Particles in liquid aren't fixed in rigid positions -- instead, they can flow right over each other.
Like liquid, gas doesn't have a defined shape -- it always ends up taking the shape of whatever container it finds itself in. Its volume isn't a sure thing, either: The volume of a certain mass of gas can and does change. Because the particles in gas move wildly, they have no relationship to one another that most tools can detect. For the same reason, though, gases can be compressed into a much smaller space than liquid or solid matter.
Plasma is similar to gas, but it's gas with so much extra energy inside its volume that the electrons -- the subatomic particles whose motion causes electricity -- have broken free from the positions they would normally hold inside different molecules. When these electrons break free, they create a special gas that acts like something "halfway between" gas and liquid, through its gaseous properties are still recognizable. You see plasma in fire, lightning, and the Northern Lights (as well as other, similar phenomena.)
Phases changes happen when energy is added or subtracted to matter; generally, the result of heating or cooling is a transformation to another form of matter, which we call "phase changes." The different kinds of phase changes take place under different conditions and all have different names. When heat is added to matter, particles speed up and spread out, while the reverse happens when heat is removed. Cold liquids freeze into solids and hot solids melt into liquids; hot solids can sometimes be sublimated into gases and cold gases may undergo deposition into solids; hot liquid can vaporize into gas and cold gas can condense into liquid, such as the condensation on the sides of a cold glass; gas ionizes into plasma and plasma becomes de-ionized to transform into normal gas -- both very rare processes. No matter what phase change matter undergoes, the chemical makeup of the matter itself does not change -- only its physical form.
By Rae Eriksen