Phase Changes in Matter - Reading

Phase Changes in Matter

What is Matter? - Reading

Paragraph 1

What is matter? Matter is made up of tiny atoms, which make up everything in the universe! The atoms combine to form larger molecules, and these atoms can be found all around us, from the chair we sit on to the water we drink. Matter can exist as a solid, liquid, or gas, depending on its thermal energy. These are known as the phases or states of matter.

Paragraph 1 Continued

Let us first think about the different states of water. Water, or H2O, is a type of molecule made up of two hydrogen atoms and one oxygen atom. We can find water in the form of solid ice, liquid water, or water vapor, which is a gas. Even though the three states of water look completely different, they are all still made of the same molecules.

Paragraph 2

Ice is very hard and has its own shape. This is because when water is in its solid state, the molecules do not move much and have relatively little energy. The electrons of each atom are still able to move, so each molecule has a slight vibration, but they remain in a fixed position. Since the molecules in a solid do not move much, they maintain a distinct shape and volume. If you were to place a cube of ice in a container, it would not change its shape to match the container; it would remain in cube form.

Paragraph 3

However, when you put liquid water into a container, it flows to conform to the shape of that container. This is because when water is in its liquid form, the molecules have more energy and are able to move around more. Even though the molecules of a liquid are able to move freely around, they are still attracted to each other. As a result, liquids have a fixed volume and will take the shape of the container they are put in but will not expand to fill the container’s total volume.

Paragraph 4

Water vapor is in a gaseous state and contains the most energy among the three states of matter. Because of all the energy, gas particles move rapidly and are far apart from each other. Gases do not have a fixed shape or volume, and if you place them in an open container, they will spread out indefinitely. However, if you put a gas in a closed container, it will expand to fill the container’s volume.

Paragraph 5

So how does matter change from one state to another? Adding thermal energy to a solid will cause the solid to start changing to a liquid and then to vapor. If you place a piece of ice on the stove and turn the heat on, the ice will first turn into a liquid and then begin to change into vapor as the temperature increases. The opposite is true if you decrease the amount of thermal energy. As you remove heat, the vapor will turn into a liquid and then back into a solid. The point at which a solid changes into a liquid is called its melting point, and the point at which liquid turns into a gas is called vaporization. If we remove heat from a gas, it condenses into a liquid, and then freezes into a solid.

Multiple Choice

Rank the states of matter from the least amount of energy to most amount of energy.

• Liquid, gas, solid

• Solid, liquid, gas

• Solid, gas, liquid

• Gas, liquid, solid

Multiple Choice

If you removed enough heat from the sample below, what would it change into?

• Solid

• Liquid

• Gas

• It would stay the same

Multiple Choice

What enables liquid water to take the shape of its container?

• The molecules of liquid water are moving but still have enough attraction to one another.

• The molecules of liquid water are held tightly together by intermolecular forces.

• The molecules of liquid water are smaller than in any other phase.

• The molecules of water move very fast and stay far away from each other.

Multiple Choice

You are sitting outside on a warm day with a cold glass of water. You notice water droplets starting to collect on the outside of the glass. What kind of phase change are you observing?

• Melting

• Condensation

• Evaporation

• Sweating

Multiple Choice

Observe the phase-change diagram of an unknown substance below. What would be the melting point of this substance?

• Between 20C and 60C

• 72C

• 123C

• Between 78C and 120C