At standard temperature and pressure (STP), one mole of any gas occupies a volume of $22.4$ liters, a fact that stems from Avogadro’s law.

Avogadro’s law, named after the scientist Amedeo Avogadro, is a fundamental principle in physical chemistry. It asserts that equal volumes of all gases, when measured at the same temperature and pressure, contain an identical number of molecules. This principle can be succinctly summarized by stating that one mole of any gas at STP occupies a volume of $22.4$ liters.

STP is defined as a temperature of $0$ degrees Celsius (or $273.15$ Kelvin) and a pressure of $1$ atmosphere. These standard conditions serve as a baseline for many calculations in chemistry, as they represent typical “room conditions.”

The relationship between moles and volume for gases at STP is direct and proportional. For instance, if you double the number of moles of a gas, its volume will also double, provided that the temperature and pressure remain constant. Conversely, if you halve the number of moles, the volume will likewise be halved. This relationship is frequently employed in calculations involving gases, such as determining the volume of gas produced in a reaction or calculating the number of moles in a specific volume of gas.

This principle is also foundational to the ideal gas law, which expresses that the pressure of a gas multiplied by its volume is proportional to the number of moles of the gas multiplied by the absolute temperature. The ideal gas law enables us to calculate any one of the four variables—volume, pressure, temperature, or number of moles—if the other three are known.

In summary, the relationship between moles and volume for gases at STP is a crucial concept in chemistry. It facilitates various calculations involving gases and is essential for understanding how gases behave under different conditions.