Generally, we talk of matter being one of three different states: solid, liquid, or gas. In this lesson, we will focus only on liquids and gases, because they have some common characteristics. Let's review the properties of the three states of matter. Can you figure out what gases and liquids have in common?
| Solid | Liquid | Gas |
|---|---|---|
| definite size and shape can't easily be compressed does not flow |
takes the shape of the container can't easily be compressed flows easily |
takes the shape and volume of the container can be compressed flows easily |
Hopefully, you noticed that a liquid and a gas flow easily—the only difference is that a liquid has a definite volume and a gas does not. Because both liquids and gases can flow and take the shape of the container, they are both called fluids. We will focus our studies in this lesson on fluids.
Question
One physical property of a substance is the density. Density is the mass per unit of volume of that substance. Is density constant for a gas?
The density of a gas would depend on the volume of that gas. Since the volume of a gas changes, the density will also change. The density of a gas generally depends on the pressure and temperature of the surrounding air. Usually, accepted values for density are given at 1 atmospheric pressure (atm) and 0°C. The density of a solid and the density of a liquid are going to be constant, regardless of how much of the substance there is. The density in those states depends only on the type of substance.
