What Happens to Molecules During a Phase Change?

By: Anjali V.
In 2nd grade, you might have talked about molecules and the 3 states of matter. But what are molecules? What are the 3 states of matter? You might know the answers, but these questions are the basic foundation of the question we are trying to figure out: What happens to molecules during a phase change?
You can see here that the three states of matter are solids, liquids, and gases.

What is matter?
Everything that takes up place is matter. We are matter. The air is matter. Matter is all around us. Matter is basically the mass of an object. Matter has 3 main states, which are call solids, liquids, and gases. For example, a solid might be an ice cube, a liquid being water, and gas as steam (or water vapor). It is hard to believe that when you breathe, you are breathing in matter. But matter is made up of something. Matter is made of molecules.

What are molecules?
Molecules are tiny little particles that make up a substance. Since all substances are matter, they are the things matter is made of. Molecules also take the properties of the substance they make up. Some substances have special kinds of molecules. For example, a chemical might have a mixture of molecules within itself. Each substance has its own molecules. People can’t see them. But people can feel them-sort of. When you hold a pencil, since it has mass and takes up space, it is matter. And since matter is made of molecules, you are technically holding hundreds of thousands of molecules.
This shows the molecules' properties/characteristics

The three states of matter have their own individual molecules. They have certain properties. Some substances have a mixture of these molecules, but they are mostly chemicals. Everything, like matter, has molecules. Here are the individual properties of molecules:
Solid molecules are tightly packed together. The molecules are bouncing off each other, but they are so densely packed, they have no room to move. It is hard to change the mass of a solid molecule. They have the most mass of any other molecule. Liquid molecules slip over each other and have room to move. They do not move very fast because they aren’t moved as much. If you shook a water bottle, the molecules will move faster because they have been set in motion. They do not change mass, but take the shape of their container. Gas molecules move at high speeds, bouncing off each other. They can change shape and be compressed easily. The more the gas molecules bounce off their container, the bigger it gets. For example, a small box has air inside. The molecules aren’t bouncing around as much as air you are blowing into a balloon. Why? You are putting more molecules in when you blow into the balloon, causing it to grow/expand.

For me, I think that molecules almost have personalities. Solids are stubborn and won't move, liquids are calm and go with the flow, and gases are high strung and hyper. This is how I think of them. Maybe you can come up you can come up with your own idea to remember molecule properties.
You probably won’t believe this, but molecules are made up of something as well. They are not the base of matter. Molecules are made up of one of the smallest things known to man. Molecules are made of atoms.

What are atoms?
Thiis shows what an atom would look like if you zoomed in.

Atoms are so small, even with the most powerful microscopes; they are still hard to see. Atoms are incredibly minuscule; scientist performed an experiment and found that if you line up 500,000 atoms together side by side, the length of them will be less than ½ a centimeter. An atom makes up a molecule, which take the properties of the substance it makes up. Atoms, on the other hand, have chemical properties which cause the molecules to take the properties of the substance. Atoms are made up of positive and negative charges. At the center of an atom, there is something called a nucleus. The nucleus can either be a positive or negative charge, depending on the properties of the substance. Surrounding the nucleus is smaller particles. They are a combination of positive and negative charges. And since opposites attract, they stick together to form the outer layer. If you think of an atom like the earth, then you can see the layers it has. The nucleus is the core. All the other layers are drawn to the center. The people and houses are the positive or negative charges surrounding the core. This is just an idea, and you can expand on it, bit this is just to help get a picture of what an atom might look like.

What is phase change?
Phase change is when one state of matter changes to another. The variable is heat. When you hear the phrase “Phase change”, it also means “State change, as in the 3 states of matter. You ca
This shows the changes between phases by adding or reducing the heat.
n change the amount of the heat and the temperature. In the diagram, you can see that the solid is the ice, the liquid being water, and steam as the gas. To change the solid (ice) to a liquid (water), you add heat and melt it. If you want to change the liquid to a solid, you freeze it. If you change a liquid to a gas, (in this case water to steam) you must add heat and boil it. To change a gas (steam) to a liquid (water) you must cool it down, and it will condense. An uncommon phase change is when a gas becomes a solid or vice-versa. As a gas turns into a solid, it is going through a change called crystallization. When a solid skips the liquid state and becomes a gas, it is called sublimation. A substance called dry ice is an example of a solid turning to a gas. The ice (the solid) is so cold, as soon as it hits air, it has a chemical reaction with the Carbon Dioxide in the air and turns right into a gas, not melting and skipping the liquid state.

What Happens to Molecules during a phase change?
Now that we know all this background information, we can find out what happens to molecules during a phase change? Molecules slow down, almost as if thinking of what to do next. Then they have a chemical reaction with the amount of heat. When we see it changing, it seems very fast. But, it is actually slow. Sometimes, molecules will change sizes as they are changing. It really depends on the heat you apply and the amount you have to change. This whole report was on this one little thing. But it really affects almost everything in nature. It is fairly simple matter, but it is a fairly big matter. This answer might be small, but knowing the background information makes you dig a little deeper and understand this topic.
In conclusion…
Phase change is not a complex matter. If you know the basics, it can take you very far. Can you imagine that this all is a natural reaction? We may create the experiment, but the outcome is not up to us. Way back when, people didn’t know these experiments, changes, and phases, even existed. With technology advancing each and every day, who knows what we’ll discover next?

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  • Nucleus: The center of an atom, has the largest fraction of mass within an atom.
  • Phase Change: A change from one state of matter to another.
  • Crystallization: Forms small crystals that solidify. (Gas to solid)
  • Sublimation: To purify/break down (Solid to gas)
  • Atoms: A mixture a positive and negative charges that attract to each other.