What is Specific Volume? - Definition, Formula & Units

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  • 0:03 What Is Specific Volume?
  • 1:12 Formula for Specific Volume
  • 2:41 Specific Volume for…
  • 5:18 Units for Specific Volume
  • 5:33 Lesson Summary
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Lesson Transcript
Instructor: Dina El Chammas Gass

Dina has taught college Environmental Studies classes and has a master's degree in Environmental and Water Resource Engineering.

In this lesson, you'll learn what specific volume is, how to calculate it for ideal gases, and what units are associated. The lesson also includes numerical examples to better understand how the calculations are done.

What Is Specific Volume?

Imagine a rock weighing 5 kg (about 11 pounds). You can probably picture the size of a rock like that - while you could carry it around, you couldn't exactly start skipping it on a lake.

Now imagine a 5 kg sponge. A sponge the same size as your rock would weigh significantly less, so a 5 kg sponge would have to be pretty huge! Therefore, though they had the same weight, they would have very different volumes.

Specific volume is a measurement of a material related to its volume and mass. It relates to solids, liquids, and gasses, and it quantifies the amount of space a certain mass of material occupies.

Specific volumes are measured for different materials at standard temperature and pressure, which is defined as 0 degrees Celsius and 1 atm (or atmosphere). So you can refer to a table of specific volumes and figure out the specific volumes for air, water, or methane, for example. Because materials expand when temperatures go up and contract when pressure increases, the value will change if your material is at a higher temperature or under pressure.

Formula for Specific Volume

To calculate specific volume you need to know the volume (V) and the mass (m). Specific volume equals volume divided by mass. Typically, volume is measured in cubic meters (m3), and mass is measured in kilograms. Specific volume is then calculated as volume divided by mass.

Notice that since density is mass over volume, specific volume can also be defined as the inverse of density. So you can also calculate specific volume by using the formula for inverse density:

Density Inverse

To better imagine this, let's say you have a container with a certain amount of air inside. If you squeeze the container without letting air out, you've effectively reduced the volume and decreased your specific volume. However, you've also increased the density.

So let's say your container is 10 gallons, or 0.038 m3, and you have 5 kg worth of air in there. The specific volume is going to be:

0.038 / 5 = 0.0076 m3/kg

Squeeze the container to 5 gallons, 0.019 m3, and your specific volume is now:

0.019 / 5= 0.0038 m3/kg

Your specific volume decreased when you decreased the volume. If your container is made bigger, the specific volume is going to increase, and your density is going to decrease.

Specific Volume for Ideal Gases

Now, let's discuss specific volume for ideal gases…

The ideal gas law is based on assumptions that greatly simplify the motion of gaseous particles. This law makes analyzing the properties of gases much more manageable. Most gases at standard temperature and pressure behave like 'ideal' gases anyway.

The ideal gas law relates pressure and volume to a gas constant, temperature and moles; moles being a way to quantify the number of atoms or molecules in your material. The gas constant R is a universal constant equal to 0.08206 L (atm) / mol (K). The ideal gas law states that:

Ideal Gas Law

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