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Carbon dioxide

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**Chemical and Physical Properties of CO2:**
– CO2 is a greenhouse gas with the formula CO2.
– Soluble in water, forming carbonate and bicarbonate.
– Concentration in the atmosphere is around 421 ppm.
– Burning fossil fuels is the primary cause of increased CO2 levels.
– Linear and centrosymmetric molecular structure.
– No electric dipole moment due to symmetry.
– Four vibrational modes observed in the infrared spectrum.
– Forms carbonic acid in aqueous solution.
– Physical properties include colorless gas, sharp odor, and various states at different pressures and temperatures.

**Biological and Environmental Impact of CO2:**
– Plants use CO2 in photosynthesis to produce oxygen.
– Burning fossil fuels is the primary cause of climate change.
– Excess CO2 emissions are absorbed by land and ocean sinks.
– CO2 can be sequestered in rocks, coal, petroleum, and natural gas.
– Plants, algae, and cyanobacteria absorb CO2 during photosynthesis.
– Elevated CO2 levels enhance crop yield but decrease micronutrient concentrations.
– Carbon fixation incorporates atmospheric CO2 into organic molecules.
– Ocean acidification affects marine calcifying organisms due to increased acidity.

**Industrial Applications and Chemical Reactions of CO2:**
– CO2 is used in welding, fire extinguishers, and as a pressurizing gas.
– Functions as a supercritical fluid solvent and in fermentation processes.
– Reactions with nucleophiles are reversible and less favored.
– Amines form carbamates in CO2 scrubbers.
– Strong nucleophiles like Grignard reagents give carboxylates.
– Acts as a ligand in metal carbon dioxide complexes.

**Biological Role, Photosynthesis, and Respiration Involving CO2:**
– End product of cellular respiration in various organisms.
– Plants absorb CO2 during photosynthesis to produce sugars and oxygen.
– RuBisCO enzyme involved in carbon fixation.
– Plants emit CO2 during respiration.
– Phytoplankton photosynthesis in oceans promotes CO2 absorption.
– Elevated CO2 levels lead to reduced water usage in plants.

**Human Health and Physiology Effects of CO2:**
– CO2 exposure can lead to drowsiness, hypercapnia, and suffocation.
– Adaptation mechanisms in humans balance blood acidification.
– Cognitive function can decrease even at low CO2 levels.
– ISS crew experienced health issues at 0.5% CO2 concentration.
– ASHRAE standards may lead to indoor CO2 concentrations up to 2,500 ppm.
– Breathing rate influences blood pH regulation and respiratory responses.

Carbon dioxide (Wikipedia)

Carbon dioxide is a chemical compound with the chemical formula CO2. It is made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature, and as the source of available carbon in the carbon cycle, atmospheric CO2 is the primary carbon source for life on Earth. In the air, carbon dioxide is transparent to visible light but absorbs infrared radiation, acting as a greenhouse gas. Carbon dioxide is soluble in water and is found in groundwater, lakes, ice caps, and seawater. When carbon dioxide dissolves in water, it forms carbonate and mainly bicarbonate (HCO3), which causes ocean acidification as atmospheric CO2 levels increase.

Carbon dioxide
Structural formula of carbon dioxide with bond length
Ball-and-stick model of carbon dioxide
Ball-and-stick model of carbon dioxide
Space-filling model of carbon dioxide
Space-filling model of carbon dioxide
IUPAC name
Carbon dioxide
Other names
  • Carbonic acid gas
  • Carbonic anhydride
  • Carbonic dioxide
  • Carbonic oxide
  • Carbon(IV) oxide
  • Methanedione
  • R-744 (refrigerant)
  • R744 (refrigerant alternative spelling)
  • Dry ice (solid phase)
3D model (JSmol)
ECHA InfoCard 100.004.271 Edit this at Wikidata
EC Number
  • 204-696-9
E number E290 (preservatives)
MeSH Carbon+dioxide
RTECS number
  • FF6400000
UN number 1013 (gas), 1845 (solid)
  • InChI=1S/CO2/c2-1-3 checkY
  • InChI=1/CO2/c2-1-3
  • O=C=O
  • C(=O)=O
Molar mass 44.009 g·mol−1
Appearance Colorless gas
  • Low concentrations: none
  • High concentrations: sharp; acidic
  • 1562 kg/m3 (solid at 1 atm (100 kPa) and −78.5 °C (−109.3 °F))
  • 1101 kg/m3 (liquid at saturation −37 °C (−35 °F))
  • 1.977 kg/m3 (gas at 1 atm (100 kPa) and 0 °C (32 °F))
Critical point (T, P) 304.128(15) K (30.978(15) °C), 7.3773(30) MPa (72.808(30) atm)
194.6855(30) K (−78.4645(30) °C) at 1 atm (0.101325 MPa)
1.45 g/L at 25 °C (77 °F), 100 kPa (0.99 atm)
Vapor pressure 5.7292(30) MPa, 56.54(30) atm (20 °C (293.15 K))
Acidity (pKa) Carbonic acid:
pKa1 = 3.6
pKa1(apparent) = 6.35
pKa2 = 10.33
−20.5·10−6 cm3/mol
Thermal conductivity 0.01662 W·m−1·K−1 (300 K (27 °C; 80 °F))
  • 14.90 μPa·s at 25 °C (298 K)
  • 70 μPa·s at −78.5 °C (194.7 K)
0 D
37.135 J/(K·mol)
214 J·mol−1·K−1
−393.5 kJ·mol−1
V03AN02 (WHO)
NFPA 704 (fire diamond)
Lethal dose or concentration (LD, LC):
90,000 ppm (162,000 mg/m3) (human, 5 min)
NIOSH (US health exposure limits):
PEL (Permissible)
TWA 5000 ppm (9000 mg/m3)
REL (Recommended)
TWA 5000 ppm (9000 mg/m3), ST 30,000 ppm (54,000 mg/m3)
IDLH (Immediate danger)
40,000 ppm (72,000 mg/m3)
Safety data sheet (SDS) Sigma-Aldrich
Related compounds
Other anions
Other cations
Related carbon oxides
See Oxocarbon
Related compounds
Supplementary data page
Carbon dioxide (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

It is a trace gas in Earth's atmosphere at 421 parts per million (ppm), or about 0.04% (as of May 2022) having risen from pre-industrial levels of 280 ppm or about 0.025%. Burning fossil fuels is the primary cause of these increased CO2 concentrations and also the primary cause of climate change.

Its concentration in Earth's pre-industrial atmosphere since late in the Precambrian was regulated by organisms and geological phenomena. Plants, algae and cyanobacteria use energy from sunlight to synthesize carbohydrates from carbon dioxide and water in a process called photosynthesis, which produces oxygen as a waste product. In turn, oxygen is consumed and CO2 is released as waste by all aerobic organisms when they metabolize organic compounds to produce energy by respiration. CO2 is released from organic materials when they decay or combust, such as in forest fires. Since plants require CO2 for photosynthesis, and humans and animals depend on plants for food, CO2 is necessary for the survival of life on earth.

Carbon dioxide is 53% more dense than dry air, but is long lived and thoroughly mixes in the atmosphere. About half of excess CO2 emissions to the atmosphere are absorbed by land and ocean carbon sinks. These sinks can become saturated and are volatile, as decay and wildfires result in the CO2 being released back into the atmosphere. CO2 is eventually sequestered (stored for the long term) in rocks and organic deposits like coal, petroleum and natural gas. Sequestered CO2 is released into the atmosphere through burning fossil fuels or naturally by volcanoes, hot springs, geysers, and when carbonate rocks dissolve in water or react with acids.

CO2 is a versatile industrial material, used, for example, as an inert gas in welding and fire extinguishers, as a pressurizing gas in air guns and oil recovery, and as a supercritical fluid solvent in decaffeination and supercritical drying. It is a byproduct of fermentation of sugars in bread, beer and wine making, and is added to carbonated beverages like seltzer and beer for effervescence. It has a sharp and acidic odor and generates the taste of soda water in the mouth, but at normally encountered concentrations it is odorless.

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