Many properties of gases do not depend upon the specific structure of the gas molecules in a sample. Properties of a gas sample that are independent of the type of gas in a sample are known as bulk properties of gases. These properties include pressure, volume, temperature and amount of substance.

The fact that these properties are largely independent of the identity of the gas in a sample has been well established through multiple experimental measurements. When analyzing various gas samples, if three of the bulk properties are the same, the fourth property will also be the same. You saw this in the example on the previous page because the fourth property, volume, was the same for each gas sample. Another example is, if two samples of different gases contain the same amount of gas at the same volume and temperature, the pressure exerted by each sample will be almost identical.

Our understanding of the bulk properties of gases has been put to good use. We are able to manipulate these properties to do work. For example, the properties of pressure and volume have been exploited in the internal combustion engine. In this important innovation that is used to power our vehicles, the expansion of gases in a cylinder is used to drive the pistons in the engine.

The bulk properties of gases are also put to use in the field of chemistry. Measurements of these properties (usually volume) allow chemists to quantify the extent of reactions that involve gases.

Why do you think that the volume of a gas sample and the pressure exerted by a gas sample are not significantly affected by the identity of the gas sample?