States of Matter: Study with Video Lessons, Practice Problems & Examples

Substances exist in three states of matter: solids, liquids, and gases, each with distinct physical properties. Gases are highly compressible and assume both the volume and shape of their containers. Liquids have moderate compressibility, taking the shape but not the volume of their containers. Solids maintain both shape and volume, exhibiting low compressibility. Viscosity, the resistance to flow, varies: gases have low viscosity, liquids have moderate viscosity, and solids have high viscosity, indicating their movement characteristics under different conditions.

States of Matter Concept 1

Under varying conditions of pressure and temperature, most substances can exist in three states of matter. So we're talking about solids, liquids, or gases. Now we're going to say these forms of matter have an effect on physical properties which deal with physical appearance or state. Now with these states of matter, we have two terms you should familiarize yourself with. We have compressibility and viscosity. Compressibility is the capacity to flatten or reduce in size by increasing pressure. So something that's incredibly compressible can have its size decreased. Usually, that is associated with gas molecules. Gas molecules spread themselves out as far as possible within a container. I can apply outward pressure on this and squeeze the gas molecules closer together. Now, viscosity. Viscosity is the resistance to flow or to change in shape. Something that is highly viscous moves very slowly, because it has a high resistance to flow. Think of honey versus water. Water can flow very easily in its liquid form. It has a low viscosity. There's not that much resistance to its flow. Honey, on the other hand, moves much more slowly, so it is more viscous. So just remember, the higher the viscosity, the higher the resistance to flow, the slower the substance will move.

States of Matter Concept 2

So here when we take a look at the 3 states of matter, we first look at gases. Gases themselves can assume both the volume and shape of their containers. Liquids, on the other hand, can assume the shape, but not necessarily the volume of their container. Let's say your volume is a 100 ml beaker, and you only have 10 ml of your liquid. You could put all that liquid within that beaker, but there just isn't enough of it to fill up the whole beaker. There's only 10 ml of it. Solids, they maintain both their shape and their volume. When it comes to gases, gases are highly compressible, so they have a high compressibility. That means that I can put them in a container, apply pressure to that container, and cause those gas molecules to come closer and closer together. That's what we mean by highly compressible. Your molecules are far enough apart that I can apply outside pressure and bring them closer together. Here, liquids, the molecules are not right next to each other as tightly. They're moving around freely. Because of this, we're going to say that they have a moderate compressibility. I could squeeze them closer together but not by much. For solids, solids are locked in place, with each other. Here, they have a low compressibility. I can't squeeze the atoms any closer together. Next, viscosity. Viscosity, remember, is our resistance to flow, something that is viscous moves very slowly. Gases move around and jump around pretty easily inside of a container. Because of this, we'll say gases have a low viscosity. Liquids like water, water kind of moves pretty quickly but not all liquids are like water. Because of this, we're going to say liquids have more of a moderate viscosity. Solids, you take a solid you like, your calculator put on the table. It's not going to move pretty easily. You have to apply force to it to move it. That's because solids generally have a high viscosity. They have a high resistance to flow. They don't want to move unless you make them move. Right? So when we take a look at our 3 phases of matter, keep in mind their shape and volume in terms of a container, their viscosity, as well as their compressibility.

States of Matter Example 1

It states that an unknown substance has a volume of 12.1 liters and, upon quadrupling the pressure, has an unchanged volume, which is the likely physical state of the unknown. Here, we have solid, liquid, gas, and neutron. Well, here, a neutron isn't one of our physical states of matter, so we can take that out. That means our answer is either a, b, or c. Here, they're telling us that we're quadrupling the pressure and the volume doesn't change at all. Remember, gases are highly compressible. So changing the pressure by this much would cause a big change in the volume of the gas. Liquids are not as compressible as gases, but they would be affected if we quadrupled the pressure. The volume would adjust slightly for liquids. So here, it can't be a liquid. It would have to be a solid. Solids themselves are not compressible in terms of applying pressure to them. The volume more or less would stay the same. So here, out of all our options, option a is the correct answer.

Which of the following choices will have the lowest observed viscosity?  

• A. Water
• B. Helium gas
• C. Molasses
• D. Tar

Nitric acid, which is used in the production of fertilizers, plastics and dyes, has a melting point of – 42ºC and a boiling point of 83ºC. Determine its physical state at a temperature of 110ºC.

• A. Solid
• B. Liquid
• C. Gas
• D. Plasma

Here’s what students ask on this topic:

What are the three states of matter and their characteristics?

The three states of matter are solids, liquids, and gases. Solids maintain both their shape and volume, exhibiting low compressibility and high viscosity, meaning they resist flow. Liquids take the shape but not the volume of their containers, have moderate compressibility, and moderate viscosity, allowing them to flow more easily than solids. Gases assume both the volume and shape of their containers, are highly compressible, and have low viscosity, meaning they flow and spread out easily.

How does compressibility differ among solids, liquids, and gases?

Compressibility refers to the ability of a substance to decrease in volume under pressure. Gases are highly compressible because their molecules are far apart and can be pushed closer together. Liquids have moderate compressibility; their molecules are closer than in gases but still have some space to be compressed. Solids have low compressibility because their molecules are tightly packed and cannot be easily compressed further.

What is viscosity and how does it vary among the states of matter?

Viscosity is the resistance of a substance to flow. Gases have low viscosity, meaning they flow easily. Liquids have moderate viscosity; for example, water flows easily, but honey flows more slowly. Solids have high viscosity, meaning they resist flow and do not move unless a force is applied. The higher the viscosity, the slower the substance moves.

How do gases, liquids, and solids behave in containers?

Gases assume both the volume and shape of their containers, spreading out to fill the entire space. Liquids take the shape of their containers but do not fill the entire volume unless there is enough liquid to do so. Solids maintain their own shape and volume regardless of the container, meaning they do not change shape to fit the container.

What is the relationship between temperature, pressure, and the states of matter?

Temperature and pressure significantly affect the states of matter. Increasing temperature generally causes substances to move from solid to liquid to gas (melting and boiling). Increasing pressure can compress gases into liquids or solids. For example, water vapor (gas) can condense into liquid water under high pressure. Conversely, reducing pressure can cause liquids to evaporate into gases. These changes are due to the energy and spacing of molecules in different states.