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Key Idea 2
Properties of Gases
Concept Question: What properties are common to all gases and how are they explained with the kinetic molecular theory?

What do we know?

As you have learned, many different types of gases exist in Earth's atmosphere. What properties of these gases are the same, and which are different?

To answer this question, let us begin by looking at the volume of gases. At ambient conditions (pressure of 1 bar and temperature of 25 °C), the experimentally determined volumes of 1 mol of various gas samples are shown below.


Carbon Dioxide (CO2)

Oxygen (O2)

Nitrogen (N2)

Hydrogen (H­2)

Sulfur Hexafluoride (SF6)

Molar Volume (L)






According to the experimental evidence, even if the identity of the gas in the sample is changed, the volume of a gas sample does not change substantially. Volume is a property that is the same for these gases.