The volume of gases is not typically expressed in grams per cubic decimeter (g dm⁻³) but rather in moles per cubic decimeter (mol dm⁻³), which is equivalent to moles per liter (mol L⁻¹).

Here's why:

* Grams per cubic decimeter (g dm⁻³) represents density, which is the mass of a substance per unit volume. While density is an important property, it's not the primary way to express the volume of gases.

* Moles per cubic decimeter (mol dm⁻³) or moles per liter (mol L⁻¹) represents molar concentration, which is the number of moles of a substance per unit volume. Molar concentration is a more useful unit for working with gases because it allows for direct comparison of the amount of gas present in different volumes.

Here's an example:

Let's say you have 1 mole of an ideal gas at standard temperature and pressure (STP). This gas will occupy a volume of 22.4 liters. The molar concentration of this gas would be 1 mol/22.4 L, which is approximately 0.045 mol L⁻¹.

In summary, g dm⁻³ is used to express density, while mol dm⁻³ or mol L⁻¹ is used to express molar concentration, which is more relevant for working with gases.