Gas

The air around us is a mixture of many different gases, but just three elements – nitrogen, oxygen and argon - form nearly all of it. Air is the raw material for producing gases. After the gases are extracted, what remains is returned to the atmosphere. Linde’s most important products are oxygen, nitrogen and argon. Gas can be compressed. Examples of gases are oxygen at room temperature (approximately 20 ºC), hydrogen at room temperature, and water at standard atmospheric pressure and a temperature above 100 ºC. If a gas in container is heated, the pressure increases. If it is cooled, the pressure drops. If the gas is placed in a sealed container and then the volume of the container is reduced, the compression heats the gas. If the volume of the sealed container increases, the decompression cools the gas.

If the temperature becomes sufficiently high, certain gases, such as hydrogen, will rapidly combine with other gases such as oxygen or chlorine. This is combustion. Some chemical reactions between gases and other substances occur more slowly; an example is the gradual oxidation of iron to form iron oxide (rust). In this case, the oxygen is gaseous at room temperature, while the iron and the iron oxide are solids. When a gas in the gaseous state is cooled to a low enough temperature, it may become a liquid or a solid. For example, if nitrogen is cooled down to a temperature far below zero Celsius , it liquefies. Another gas, carbon dioxide, becomes a solid known as dry ice, skipping the liquid phase. Some gases are lighter than air, for example helium and hydrogen, and can thereby be used for lifting solid objects, like balloons or even vessels.