Chemistry

The Chemical Properties of Carbon Dioxide



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At atmospheric conditions of standard temperature and pressure, carbon dioxide is a gas.  It is a covalently bonded molecule composed of one carbon atom and two oxygen atoms, whose chemical symbol is CO2.  It is colorless and odorless, and is a small constituent of air.  Although its concentration in air varies slightly, a typical concentration in air is about .038% or 380 ppm (parts per million). 

The Flemish scientist Jan Baptista van Helmont (circa 1850 – 1644) is credited with the discovery of carbon dioxide.  He identified a gas that was formed during the combustion of wood, which is known today to be carbon dioxide.  His discovery was important not only for the discovery of the gas, but also because he first understood that air is a combination of gases.  The Scottish scientist Joseph Black (1728 – 1799) also did many studies with carbon dioxide gas, and discovered that it is exhaled in human breath.

Because of its properties, carbon dioxide gas has many practical and industrial applications.  Frozen carbon dioxide is known as “dry ice”.  Carbon dioxide gas freezes to this solid form at –78.5 degrees C (Centigrade).  When thawed at atmospheric conditions,  it does not go through a liquid stage, but changes directly to a gas.  This is called sublimation.  Dry ice is useful as a cooling agent and can save the frozen food in a freezer during a power failure. 

In manufacturing and construction, carbon dioxide is used as a shield gas in welding, because the gas protects the molten weld puddle against oxidation by the surrounding air.  Since carbon dioxide is reactive and can create some oxidation, a mixture of carbon dioxide and argon, an inert gas, is usually used.  

In the oil industry, carbon dioxide is used to simplify extraction from wells.  It is pumped into the wells and partially dissolved into the oil, reducing its viscosity so that it can be extracted more easily. 

Carbon dioxide is also used as an aerosol propellant.  It is a safer replacement for the previous chlorofluorocarbons (CFCs) that were used in aerosols in the past and have been named as causes of the depletion of the ozone layer in the Earth’s stratosphere. It is used primarily in aerosol products that are designed to deliver a coarse spray at close range, such as household disinfectants.  Carbon dioxide is also used in fire extinguishers to displace the oxygen that is required for fire to burn. 

Carbon dioxide gas is used to put the “fizz” in soft drinks.  This improves the taste of the beverage and also increases the shelf life.  In health care, carbon dioxide is used as an additive to oxygen to provide a respiratory stimulant. 

In recent years, there has been concern about carbon dioxide as one of the “greenhouse gases”.   There is a natural balance of carbon dioxide in the atmosphere from the activity of plants, animals and bacteria.  Greenhouse gases such as carbon dioxide cause the earth to warm because they absorb radiation from the sun.  The double bonds in carbon dioxide molecules absorb the radiation and then transfer it to kinetic energy, which is re-emitted as heat, warming the atmosphere.  This is vital for all life on earth, but carbon dioxide is also produced from the combustion of fossil fuels used for energy, and the industrial activities of humans has upset this natural balance.  Its concentration in the Earth’s atmosphere has risen by more than 35% since many global nations have become industrialized.  The rate of increase is currently thought to be about 2 ppm per year. 

But even this rate of increase is also increasing.  An American scientist, Charles Keeling (1928 – 2005)  was affiliated with the Scripps Institute of Oceanography.  He began to systematically make monthly measurements of atmospheric carbon dioxide in 1958.  This data came to be known as “The Keeling Curve”.   This curve clearly shows that the amount of carbon dioxide in the atmosphere is increasing.  If the trend continues, the concentration of carbon dioxide will be 400 ppm within the next ten years. 

Indeed, much mainstream research shows that the earth is warming.  Its average temperature has risen by 1.4 degrees F over the past century, and it is projected to rise another 2 to 11.5 degrees F (Fahrenheit) over the next hundred years. The impacts of this kind of temperature change could be devastating.  Oceans become more acidic, causing increased erosion of coastal shorelines.  Floods and droughts caused by increased temperatures can alter and reduce crop yields.  The water cycle is already beginning to change, with rainfall during the most intense 1% of storms increased by almost 20%.  In a warmer climate, energy demands for air conditioning and electricity are increased as well. 

So it is not difficult to see that the importance of carbon dioxide gas goes well beyond its ability to make soda pop fizzy.  Above and beyond its many practical uses, it is part of a sensitive, natural balance that has evolved to make human, plant and animal life on earth possible.  Those who lead human societies would be well-advised to accept the knowledge that carbon dioxide is a gas that must be understood and is worthy of respect. 

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