The Chemical Makeup of a Gas

Importance

• Gases are an important part of the world. They allow large volumes of chemicals to travel to places that would normally be inaccessible. For example, some deserts may remain dry if gases did not carry water molecules to the parched land. Also, gases can carry solids and liquids with them under windy conditions.

Atmosphere Composition

• Nitrogen is the most common gas in the atmosphere, making up 78 percent. The form of nitrogen that mostly makes up the atmosphere is a compound of two nitrogen atoms. The next largest concentration in the air is oxygen, which makes up almost 21 percent. The remaining gases make up much smaller amounts, with argon making up 0.9 percent, carbon dioxide accounting for 0.033 percent and helium, methane, neon, krypton, nitrogen oxide, hydrogen, xenon and the ozone found in trace amounts of the air. Ozone, for example, makes up 0.000001 percent. These concentrations are found in dry air under normal conditions.

Humidity

• Water evaporates and mixes with the air, making it humid. The water vapor can range from 0.1 percent to 6 percent or higher. Water consists of two hydrogen atoms combined with one oxygen atom. These atoms are held together by a covalent bond. When temperatures increase, more water evaporates and enters into the atmosphere, increasing the humidity. This process reverses when temperatures fall, causing the water to condense and usually fall as rain. Since water transfers heat energy, humidity can influence how hot or cold the air feels.

Combustion

• Combustion changes the chemical composition of air by taking objects that would normally be solid and turning them into gases. This process can change the chemical composition of elemental compounds by breaking apart compounds and producing heat and light. For example, when a tree burns many of its particles change their chemical nature and rise into the air, becoming different gases. Many of these gases are very toxic.

Industrial Processes

• Gases that are normally not found in high quantities in the atmosphere can be extracted from nature using industrial processes. These gases are sometimes compressed in cylinders for storage purposes and are later released, either when needed to perform a certain task or unintentionally, such as with industrial byproducts. This temporarily changes the chemical composition of the air. For example, an oxygen cylinder can release oxygen on an airplane, allowing passengers to breath at altitudes that would normally have lower levels of oxygen.