Composition of air components
Layering
Discovery History
Quality Level
Relative Humidity
function
Air surrounding the Earth
This entry is a polysemous word, with 11 meanings elaborated.
Air (, the "breath of life" that we breathe every day, is layered over the Earth's surface, transparent, colorless, and odorless. It is mainly composed of nitrogen and oxygen, and it has a significant impact on human survival and production.
Air refers to the mixture of gases in the earth's atmosphere, so air is a mixture, which is mainly composed of nitrogen, oxygen, rare gases ) helium, neon, argon, krypton, xenon, ra ( don, carbon dioxide and other substances ) such as water vapor, impurities, etc (. Among them, the volume fraction of nitrogen is about 78%, the volume fraction of oxygen is about 21%, the volume fraction of rare gases ) helium, neon, argon, krypton, xenon, radon ( is about 0.934 ) (2017%, and the volume fraction of carbon dioxide is about 0.04%. The volume fraction of other substances ) such as water vapor, impurities, etc., ( is about 0.002%. The composition of air is not fixed, and as the altitude changes, the air pressure changes, and the composition ratio of the air also changes. But for a long time, people thought that air was a single substance, until later the French scientist Lavoisier first came to the conclusion that air is composed of oxygen and nitrogen through experiments. At the end of the 19th century, scientists discovered through a large number of experiments that there were rare gases such as helium, argon, and xenon in the air.
Air is colorless and odorless in its natural state.
Oxygen in the air is essential for all aerobic organisms. All animals need to breathe oxygen, and the respiration of green plants also requires oxygen. In addition, green plants use carbon dioxide from the air for photosynthesis, and the air is almost the only source of carbon dioxide needed by all plants.
Chinese Name
Air
Foreign Name
air, atmosphere
Molecular weight
28.959) average (
water-soluble
Slightly soluble
Density
Approximately 1.293 kg/m³
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Physical properties
Air is colorless and odorless, in a gaseous state.
The air density of )1.01×10Pa( 3 is 1.29 kg/m³ at 0°C and one atmosphere. The state of the gas at 0°C and one standard atmospheric pressure is called the standard state, and the air in the standard state can be regarded as an ideal gas, and its molar volume is 22.4 L/mol.
The specific heat capacity of air is related to temperature, when the temperature is 250K, the specific heat capacity of air at constant pressure cp=1.003kJ/)kg· K(, at 300K, the specific heat capacity of air at constant pressure cp=1.005kJ/)kg· K(。
The impedance of air is about 377 ohms.
Air at room temperature is a colorless and odorless gas, while liquid air is a light blue liquid that flows easily. Generally, when air is liquefied, carbon dioxide has already been removed, so the composition of liquid air is 20.95% oxygen, 78.12% nitrogen, and 0.93% argon, with other components present in negligible amounts.
The speed of sound in air at standard conditions is 331.5 m/s.
The molar mass of dry air is 28.9634 g/mol.
Under standard conditions, the refractive index of air for visible light is about 1.00029. It varies with atmospheric pressure, temperature, and air composition. In particular, humidity has a significant effect on the refractive index, and correspondingly, the speed of light in air also changes.
Specific heat capacity:
= 1.005 kJ/)kg·K( = 0.279 kWh/)Tonne K( isobaric process)
= 0.718 kJ/(kg·K) = 0.199 kWh/(Tonne K)( isothermal process )
Dry air, which does not contain water vapor, is referred to as dry air. The gas constant of dry air is 2.8704×10, the average molecular weight is 28.966, the specific heat at constant pressure is 7R/2=0.240 cal·g·K, and the specific heat at constant volume for dry air is 5R/2=0.171 cal·g·K.
Components
Volume content
Nitrogen: 78.09%
Oxygen: 20.95%
Noble gases: 0.932%
Carbon Dioxide: 0.034%
Water vapor and impurities: 0.02%
Air is a mixture of various gases. Its constant components are oxygen, nitrogen, and noble gases, while its variable components include carbon dioxide and water vapor, which can vary slightly within a small range depending on geographical location and temperature. As for the indefinite components in the air, they vary by region; for example, areas near metallurgical plants may contain sulfur dioxide, while areas near chlorine-alkali plants may contain chlorine, and so on. Additionally, there are trace amounts of hydrogen, ozone, nitrogen dioxide, methane, and varying amounts of dust in the air.
Experiments have shown that the percentage of constant components in the air remains almost unchanged at altitudes within 100 km above the ground. For example, by volume, oxygen accounts for about 20.95%, nitrogen about 78.09%, and rare gases about 0.934%.
Generally speaking, the composition of air is relatively fixed. This is very important for the survival of humans and other plants and animals. However, with the development of modern industry, harmful gases and smoke emitted into the air have changed the composition of the air, causing air pollution. Polluted air can severely harm human health, affect crop growth, and cause damage to natural resources and buildings.
Harmful substances emitted into the air can be broadly divided into two categories: particulate matter and gases. Globally, the most common gaseous pollutants emitted into the air include sulfur dioxide, carbon monoxide, and nitrogen dioxide. These gases primarily originate from the combustion of fossil fuels like coal and oil, as well as from factory exhaust.
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