Question

Why is the density of a gas much lower than that of a liquid or solid under atmospheric conditions? What units are normally used to express the density of gases?

Short answer

The density of a gas is much lower than that of a liquid or solid due to the spread out arrangement of its particles or molecules, especially under atmospheric conditions where the gas molecules disperse to occupy the entire available volume. The commonly used units to express the density of gases are kilograms per cubic meter (kg/m3) or grams per liter (g/L).

Step-by-step solution

Understand State of Matter Properties

Matter exists in three primary states - solid, liquid, and gas. Differences in density between these states can be attributed to differences in the arrangement of their respective particles or molecules. In solids and liquids, particles are closely packed together whereas in gases, particles are scattered, occupying more space. This leads to gases having a lower density than liquids and solids as density is defined as mass per unit volume.

Recognize Atmospheric Conditions Impact

Under atmospheric conditions, as the exercise stipulates, the difference in density becomes even more apparent. Gases expand to fill their containers, meaning under standard conditions, the molecules of a gas are spread out even more, resulting in a lower density.

Know The Units For Gas Density

Typically, the density of gases is expressed in kilograms per cubic meter (kg/m3) or grams per liter (g/L).