The content of carbon dioxide in the air is about 0.03%, which is one of the survival elements of nature.

Carbon dioxide is the food of plants. Under sunlight, the chlorophyll in each leaf can convert the dioxide absorbed by the leaves and the water transported from the roots into sugar, starch and oxygen. In this process, the energy in sunlight is absorbed and becomes the energy stored in starch, which becomes the energy for life activities on the earth. Carbon dioxide and green plants realize the transformation of light energy and bioenergy.

Carbon dioxide is colorless, slightly pungent and slightly sour gas under normal temperature and pressure. Carbon dioxide becomes a colorless liquid under cooling and pressure, and becomes a solid called "dry ice" when the temperature is lower. Therefore, we are exposed to carbon dioxide in three states: gas, liquid and solid.

Carbon dioxide is not toxic, but it cannot provide respiration. If you inhale too much carbon dioxide, it will hinder the discharge of carbon dioxide in the blood, making metabolism unable to carry out normally.

Carbon dioxide does not support combustion, and because its density is heavier than air, it can isolate air by covering to achieve the purpose of flame retardancy. Therefore, carbon dioxide is a widely used fire extinguishing agent. Under normal pressure and temperature above - 78.5 ℃, solid carbon dioxide directly changes into carbon dioxide gas without liquid. In the process of gasification, it needs to absorb a lot of heat without any residue, which makes dry ice a good food preservative.

The gas carbon dioxide has a certain solubility in water. One volume of water can dissolve about one volume of carbon dioxide. The solubility increases with the increase of pressure. The beverage industry uses this property to produce palatable beer and carbonated drinks.

Carbon dioxide is also the sculptor of nature. When the spring water containing carbon dioxide flows through limestone, the rocks in some places will be dissolved and become many karst caves; In some places, calcium bicarbonate in water is decomposed to form calcium carbonate for precipitation. Over the years, stalactites and stalagmites have formed, forming a variety of unique landscapes.

Carbon dioxide is rich in nature, mainly produced by burning carbon containing substances and animal metabolism. Carbon dioxide is also contained in some natural gas or oil field associated gas and carbonate formed ores.

The recovered and purified carbon dioxide is widely used in carbonated drinks, welding, cleaning, fire protection and other fields. At present, many * * * people are committed to using it as chemical raw materials.

80% of the carbon dioxide in the atmosphere comes from the respiration of people, animals and plants, and 20% comes from the combustion of fuel. 75% of the carbon dioxide scattered in the atmosphere is absorbed and dissolved in the water by the sea, lakes, rivers and other surface water and air precipitation. Another 5% of carbon dioxide is converted into organic substances through plant photosynthesis for storage. This is why the proportion of carbon dioxide in air has remained unchanged for many years.

But in recent decades, due to the rapid increase of population and the rapid development of industry, the carbon dioxide produced by breathing and the carbon dioxide produced by the combustion of coal, oil and natural gas far exceeds the previous level. On the other hand, due to deforestation, a large number of farmland has been built into cities and factories, destroying vegetation and reducing the conditions for converting carbon dioxide into organic matter. In addition, the surface water area is gradually shrinking and the precipitation is greatly reduced, which reduces the conditions for absorbing dissolved carbon dioxide and destroys the dynamic balance of carbon dioxide generation and transformation, thus increasing the carbon dioxide content in the atmosphere year by year. The increase of carbon dioxide content in the air. According to the research, the climate warming in the past hundred years is mainly due to the significant increase of carbon dioxide concentration in the atmosphere. Carbon dioxide is the main gas leading to the greenhouse effect*** The treatment of emissions and recycling is a long-term problem facing the world.

Carbon dioxide in three states

Gaseous carbon dioxide

⊙ Colorless and tasteless

⊙ It has bacteriostatic effect

⊙ Non combustible and non combustion supporting

⊙ Density is 1.5 times of air

⊙ High solubility in water

Liquid carbon dioxide

⊙ Cannot exist under normal pressure

⊙ It becomes a mixture of solid and gas in a short time when reducing pressure

⊙ With solvent properties similar to hexane

⊙ In supercritical state, it becomes an excellent solvent

Dry ice (solid carbon dioxide)

⊙ Dry ice is carbon dioxide in frozen state

⊙ Dry ice has a very low temperature (- 78.5 ℃)

⊙ Under normal pressure, dry ice cannot be converted into liquid but directly sublimates into gas.