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Carbon dioxide

Model of the carbon dioxide moleculeModel of the carbon dioxide moleculeCarbon dioxide (chemical formula CO2) is a colourless gas. It consists of a carbon atom covalently bonded to two oxygen atoms. It is about 60% denser than air. CO2 is soluble in water, in which it forms carbonic acid (H2CO3), a weak acid. At normal air pressure and low temperatures (below -78.5°C, or -109.3°F) it turns directly into a solid, commonly called dry ice. This turns back into a gas, in a process called sublimation, at temperatures higher than -78.5°C. CO2 occurs naturally in the Earth's atmosphere in tiny quantities, but these are rising rapidly.

Hot springs in Yellowstone National ParkHot springs in Yellowstone National Park


Natural sources of CO2 include volcanoes, geysers and hot springs. CO2 also occurs naturally dissolved in water. It is also present in oil and natural gas, and it can be formed from carbonate rocks such as chalk and limestone (when the rocks are dissolved in water). 

The human body produces approximately 1.0 kg (2.3 pounds) of carbon dioxide per day per person. This contains 290 g (0.63 pounds) of carbon.

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