What is the chemical formula for carbon dioxide, and what atoms does it consist of?

Carbon dioxide has the chemical formula CO2. It is composed of molecules where each carbon atom is covalently double-bonded to two oxygen atoms.

How is carbon dioxide described in terms of its state and odor at room temperature and typical concentrations?

At room temperature, carbon dioxide is a colorless gas. At normally encountered concentrations, it is odorless.

What is the primary role of atmospheric CO2 in the carbon cycle and for life on Earth?

As the primary source of carbon for life on Earth, atmospheric CO2 is a crucial component of the carbon cycle.

How does carbon dioxide interact with infrared radiation, and what is its function in Earth's atmosphere?

Carbon dioxide is transparent to visible light but absorbs infrared radiation, acting as a greenhouse gas that helps regulate Earth's temperature.

Where can carbon dioxide be found dissolved in water on Earth?

Carbon dioxide is soluble in water and can be found in groundwater, lakes, ice caps, and seawater.

What is the approximate concentration of carbon dioxide in Earth's atmosphere as of July 2025, and how does this compare to pre-industrial levels?

As of July 2025, the concentration of carbon dioxide in Earth's atmosphere is approximately 428 parts per million (ppm), or about 0.043%. This is an increase from the pre-industrial level of around 280 ppm, or 0.028%.

What is the main human activity responsible for the increase in atmospheric CO2 concentrations, and what is its primary consequence?

The burning of fossil fuels is the main cause of increased CO2 concentrations in the atmosphere, which is the primary driver of climate change.

How did organisms and geological features regulate atmospheric CO2 concentrations in Earth's pre-industrial atmosphere?

Prior to the Industrial Revolution, atmospheric CO2 concentrations were regulated by organisms and geological features, particularly since the late Precambrian period.

Describe the process by which plants, algae, and cyanobacteria utilize carbon dioxide.

Plants, algae, and cyanobacteria use energy from sunlight to synthesize carbohydrates from carbon dioxide and water through photosynthesis, releasing oxygen as a byproduct.

How do aerobic organisms release carbon dioxide?

Aerobic organisms release CO2 as a waste product when they metabolize organic compounds to produce energy through respiration, consuming oxygen in the process.

What happens to carbon dioxide when it dissolves in water, and what is the consequence of increased atmospheric CO2 levels on oceans?

When carbon dioxide dissolves in water, it forms carbonate and bicarbonate ions, leading to ocean acidification as atmospheric CO2 levels rise.

How does the density of carbon dioxide compare to dry air?

Carbon dioxide is approximately 53% denser than dry air, meaning it is heavier and tends to sink.

What happens to carbon dioxide when it is absorbed by land and ocean carbon sinks?

About half of the CO2 emissions released into the atmosphere are absorbed by land and ocean carbon sinks, where the carbon is eventually sequestered in rocks and organic deposits like coal and petroleum.

What is the primary commercial use of carbon dioxide produced by humans?

The vast majority of CO2 produced by humans goes into the atmosphere, with less than 1% being used commercially, primarily in the fertilizer industry for urea production and in the oil and gas industry for enhanced oil recovery.

What is the molecular structure of carbon dioxide, and what is the length of its carbon-oxygen bond?

Carbon dioxide molecules have a linear structure with a bond length of 116.3 pm between the carbon and oxygen atoms.

Why does a carbon dioxide molecule not possess an electric dipole moment?

Due to its linear and centrosymmetric molecular structure, a carbon dioxide molecule does not have an electric dipole moment.

What are the four vibrational modes of a carbon dioxide molecule?

Carbon dioxide has four vibrational modes: symmetric stretching, antisymmetric stretching, and a degenerate pair of bending modes.

Which vibrational modes of CO2 are observable in infrared (IR) spectroscopy, and which are observable in Raman spectroscopy?

The antisymmetric stretching mode (2349 cm⁻¹) and the degenerate bending modes (667 cm⁻¹) are observed in IR spectroscopy, while the symmetric stretching mode (1388 cm⁻¹) is detected in Raman spectroscopy.

What is the equilibrium constant for the hydration of carbon dioxide in water at 25°C?

The hydration equilibrium constant (Kh) for carbon dioxide in water at 25°C is 1.70 × 10⁻³.

How does the pH of water affect the distribution of dissolved carbon dioxide species?

In neutral to slightly alkaline water (pH > 6.5), bicarbonate predominates. In very alkaline water (pH > 10.4), carbonate becomes the predominant form.

What is the true first acid dissociation constant (pKa1) for carbonic acid?

The true first acid dissociation constant (pKa1) for carbonic acid is 3.6, although an apparent value of 6.35 is often quoted due to the assumption that all dissolved CO2 is carbonic acid.

How does carbonic anhydrase relate to carbon dioxide in biological systems?

The enzyme carbonic anhydrase catalyzes the production of carbonic acid from carbon dioxide within organisms.

What happens to the electrical conductivity of desalinated water when carbon dioxide dissolves in it?

When carbon dioxide dissolves in desalinated water, the electrical conductivity increases significantly, from below 1 μS/cm to nearly 30 μS/cm.

What is the electrophilic reactivity of carbon dioxide compared to other compounds?

Carbon dioxide is a potent electrophile, with reactivity comparable to benzaldehyde or strongly electrophilic α,β-unsaturated carbonyl compounds.

What types of nucleophiles can react with carbon dioxide to form carboxylates?

Only very strong nucleophiles, such as the carbanions provided by Grignard reagents and organolithium compounds, can react with CO2 to yield carboxylates.

What is the redox potential for the reduction of CO2 to CO near pH 7?

The redox potential for the reduction of CO2 to CO near pH 7 is approximately -0.53 V versus the standard hydrogen electrode.

What is the common name for solid carbon dioxide, and at what temperature does it sublime at 1 atm?

Solid carbon dioxide is commonly known as dry ice. It sublimes directly to a gas at temperatures below 194.6855 K (−78.4645 °C) at a pressure of 1 atm.

Under what pressure conditions does carbon dioxide form a liquid state?

Carbon dioxide only forms a liquid state at pressures above 0.51795 MPa (5.11177 atm).

What is "carbonia," and how is it formed?

Carbonia is an amorphous, glass-like solid form of carbon dioxide produced by supercooling heated CO2 at extreme pressures (40–48 GPa) in a diamond anvil.

What is the biological role of carbon dioxide in organisms that respire aerobically?

Carbon dioxide is an end product of cellular respiration in aerobic organisms, produced when they break down sugars, fats, and amino acids with oxygen to generate energy.

How is carbon dioxide transported in human blood?

CO2 is transported in blood primarily as bicarbonate ions (about 70-80%), dissolved in blood plasma (5-10%), and bound to hemoglobin as carbamino compounds (5-10%).

What is the Haldane Effect in relation to hemoglobin and CO2 transport?

The Haldane Effect describes how the binding of CO2 to hemoglobin decreases the amount of oxygen bound for a given partial pressure of oxygen, which is important for CO2 transport from tissues to lungs.

How does carbon dioxide regulate blood supply locally?

Carbon dioxide acts as a local regulator of blood supply by causing capillaries to expand when its concentration is high, thereby increasing blood flow to the tissue.

What is the primary stimulus for breathing in humans?

Higher carbon dioxide levels, rather than low oxygen levels, are the primary stimulus for breathing in humans.

What is the typical partial pressure of carbon dioxide in arterial blood?

The typical partial pressure of carbon dioxide in arterial blood ranges from 4.7 to 6.0 kPa (35 to 45 mm Hg).

What is the primary driver of the current increase in atmospheric CO2 concentrations?

The primary driver of the current increase in atmospheric CO2 concentrations is the burning of fossil fuels.

How does carbon dioxide contribute to Earth's greenhouse effect?

Carbon dioxide absorbs and emits infrared radiation at specific wavelengths, trapping heat near the surface and warming Earth's surface and lower atmosphere.

What is the significance of phytoplankton in the oceanic carbon cycle?

Photosynthesis by phytoplankton consumes dissolved CO2 in the upper ocean, which in turn promotes the absorption of CO2 from the atmosphere.

What is ocean acidification, and what is its primary cause?

Ocean acidification is the ongoing decrease in the pH of Earth's oceans, primarily caused by the absorption of carbon dioxide emissions from human activities.

How does ocean acidification affect marine calcifying organisms?

Ocean acidification reduces the concentration of carbonate ions in seawater, making it harder for marine calcifying organisms like mollusks and corals to build shells and skeletons out of calcium carbonate.

What is the primary source of CO2 used in enhanced oil recovery (EOR)?

Most CO2 injected for EOR comes from naturally occurring underground deposits, though some is captured from industrial facilities.

How is carbon dioxide utilized in agriculture, specifically in greenhouses?

Carbon dioxide is added to greenhouse atmospheres to sustain and increase plant growth rates through photosynthesis.

What is the function of carbon dioxide as a food additive?

Carbon dioxide is used in the food industry as a propellant and an acidity regulator, listed as E290 in the EU.

How does carbon dioxide contribute to the taste and sensation of carbonated beverages?

Dissolved carbon dioxide converts to carbonic acid, contributing a sour taste, and also induces a somatosensory response, creating the characteristic sensation of carbonation.

What is the role of dry ice in winemaking?

Dry ice is used in winemaking to rapidly cool grape clusters after harvest, preventing premature fermentation and preserving sugar concentration, and also for carbonic maceration.

How is carbon dioxide used in welding, and what are the potential drawbacks?

Carbon dioxide is used as an atmosphere in welding (often called MAG welding), but it can react at high temperatures, potentially causing welds to be more brittle than those made in inert atmospheres.

Why is carbon dioxide a common compressed gas for pneumatic systems and consumer products?

CO2 is used because it is inexpensive, non-flammable, and undergoes a phase transition to liquid at room temperature under attainable pressures, allowing more gas to be stored in a container.

How do carbon dioxide fire extinguishers work, and what are their limitations?

CO2 fire extinguishers extinguish flames by displacing oxygen, starving the fire. They are effective on electrical and flammable liquid fires but less so on ordinary combustibles as they don't cool the material significantly.

What is supercritical carbon dioxide, and what are its applications?

Supercritical carbon dioxide exists at temperatures and pressures above its critical point and is used as a solvent in applications like decaffeinating coffee and in the pharmaceutical industry as a less toxic alternative to organochlorides.

What is the significance of carbon dioxide in the operation of CO2 lasers?

Carbon dioxide serves as the lasing medium in carbon-dioxide lasers, which are an early and widely used type of laser.

How was carbon dioxide first described as a discrete substance?

In the 1640s, Jan Baptist van Helmont observed that burning charcoal in a closed vessel produced an invisible substance he termed "gas" or "wild spirit," which was later identified as carbon dioxide.

Carbon Dioxide Wiki: The Carbon Cycle's Cornerstone: Understanding Carbon Dioxide

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Understanding Carbon Dioxide

Chemical Identity

Carbon dioxide is a chemical compound with the formula CO₂. It comprises molecules where a single carbon atom is covalently double-bonded to two oxygen atoms. At standard temperature and pressure, it exists as a colorless gas, typically odorless at common concentrations.^[1]

Biological Significance

As the primary carbon source for life on Earth, atmospheric CO₂ is fundamental to the carbon cycle. Plants, algae, and cyanobacteria utilize it in photosynthesis to synthesize carbohydrates, releasing oxygen as a byproduct.^[13]

Atmospheric Role

CO₂ is transparent to visible light but absorbs infrared radiation, functioning as a potent greenhouse gas. Its increasing concentration in Earth's atmosphere is the primary driver of contemporary climate change.^[12]

Chemical and Physical Properties

Molecular Structure

The carbon dioxide molecule possesses a linear and centrosymmetric structure. The carbon-oxygen bond length is approximately 116.3 pm. Due to its symmetry, it lacks a permanent electric dipole moment. Its molecular vibrations, including symmetric and antisymmetric stretching and degenerate bending modes, are detectable via infrared and Raman spectroscopy.^[19]

Behavior in Aqueous Solution

Carbon dioxide exhibits solubility in water, reversibly forming carbonic acid (H₂CO₃), a weak acid. The equilibrium favors dissolved CO₂ over carbonic acid at neutral pH. At higher pH levels, bicarbonate (HCO₃^-) and carbonate (CO₃^2-) ions become predominant, influencing ocean chemistry and acidification.^[23]

Key Physical Data

CO₂ transitions directly between solid and gas phases at atmospheric pressure (sublimation). Liquid CO₂ exists only above 0.51795 MPa. Its critical point is at 304.128 K and 7.3773 MPa. The gas is denser than air (approx. 1.53 times).^[2]

Selected physical properties of CO₂:

Property	Value
Molar Mass	44.009 g/mol
Density (gas, 1 atm, 0°C)	1.977 kg/m³
Triple Point	216.592 K (−56.558 °C)
Critical Point	304.128 K (30.978 °C)
Solubility in Water (25°C, 1 atm)	1.45 g/L
Vapor Pressure (20°C)	5.7292 MPa

Biological Role and Processes

Photosynthesis and Carbon Fixation

Carbon dioxide is indispensable for photosynthesis, the process by which photoautotrophs convert light energy into chemical energy. The enzyme RuBisCO facilitates carbon fixation, incorporating atmospheric CO₂ into organic molecules like glucose. This forms the base of most terrestrial and aquatic food webs.^[31]

Plant Growth and Climate

Elevated atmospheric CO₂ concentrations can stimulate plant growth and increase water-use efficiency. However, this enrichment may also alter nutrient content and potentially lead to shifts in vegetation composition, impacting ecosystem dynamics.^[36]^[37]

Respiration and Decomposition

CO₂ is a metabolic end-product of cellular respiration in aerobic organisms. It is also released during the decomposition of organic matter. While mature forests can be carbon sinks, decomposition and wildfires can return stored carbon to the atmosphere.^[14]^[16]

Sources of Carbon Dioxide

Anthropogenic Sources

The primary anthropogenic source of atmospheric CO₂ is the combustion of fossil fuels (coal, oil, natural gas) for energy. Other significant contributors include cement production, deforestation, and biomass burning.^[82]

Biological and Geological Processes

Naturally, CO₂ is produced through cellular respiration, fermentation, volcanic activity, and the decomposition of organic matter. Geological processes, such as the thermal decomposition of limestone (CaCO₃), also release CO₂.^[103]

Industrial Byproducts

CO₂ is generated as a byproduct in various industrial processes, including the production of hydrogen via steam reforming, ammonia synthesis, and the fermentation involved in brewing alcoholic beverages and producing bioethanol.^[101]

Commercial and Industrial Applications

Agriculture and Fertilizers

A substantial portion of commercially captured CO₂ is utilized in the fertilizer industry for urea production. Additionally, CO₂ enrichment in greenhouses enhances plant growth rates.^[116]^[118]

Enhanced Oil Recovery (EOR)

Supercritical CO₂ is injected into oil reservoirs to reduce oil viscosity and increase extraction efficiency, a process known as Enhanced Oil Recovery (EOR). This is a major commercial application, often utilizing naturally sourced CO₂.^[114]

Food, Beverages, and Other Uses

CO₂ is widely used for carbonating beverages (soft drinks, soda water) and as a food additive (E290). Other applications include metal fabrication, cooling (dry ice), fire suppression, and as a propellant.^[105]

Human Physiology and Respiration

Transport in Blood

The body produces CO₂ as a metabolic byproduct. It is transported in the blood primarily as bicarbonate ions (approx. 70-80%), with smaller amounts dissolved in plasma (5-10%) and bound to hemoglobin as carbamino compounds (5-10%). The Haldane and Bohr effects describe the interplay between CO₂, oxygen, and hemoglobin binding.^[73]

Regulation of Respiration and pH

Carbon dioxide levels are a primary stimulus for respiration. The body maintains blood pH homeostasis through bicarbonate buffering. Deviations in breathing rate can lead to respiratory acidosis (low breathing rate, high CO₂) or respiratory alkalosis (high breathing rate, low CO₂).^[75]

Typical partial pressures of carbon dioxide (pCO₂) in humans:

Blood Compartment	kPa	mm Hg
Venous Blood	5.5–6.8	41–51
Arterial Blood	4.7–6.0	35–45

Environmental Impact and Climate

Greenhouse Gas Effect

Carbon dioxide is a principal greenhouse gas, absorbing and re-emitting infrared radiation. This process traps heat in Earth's lower atmosphere, contributing significantly to the planet's warming trend and influencing global climate patterns.^[83]

Ocean Acidification

The absorption of excess atmospheric CO₂ by oceans leads to ocean acidification. This process lowers seawater pH, reducing the availability of carbonate ions essential for marine organisms like corals and mollusks to form shells and skeletons.^[90]^[92]

Atmospheric Concentration Trends

Atmospheric CO₂ concentrations have risen dramatically since the Industrial Revolution, primarily due to human activities. Current levels (over 420 ppm) are the highest in millions of years, driving significant environmental changes.^[79]^[80]

Atmospheric CO₂ concentration measured at Mauna Loa Observatory:

Pre-industrial levels: ~280 ppm
Current levels (approx.): ~427 ppm
Historical context: Highest in 14 million years.^[87]

Toxicity and Safety Thresholds

Health Effects of High Concentrations

Elevated CO₂ concentrations can cause hypercapnia and respiratory acidosis. Symptoms range from dizziness and headaches at moderate levels (e.g., 10,000 ppm) to unconsciousness and death at higher concentrations (e.g., >70,000 ppm).^[47]

Indoor Air Quality

Inadequate ventilation in enclosed spaces leads to increased indoor CO₂ levels, impacting occupant health, comfort, and cognitive function. Occupational exposure limits are set to mitigate these risks.^[53]

Effects of CO₂ concentration in air:

Concentration (ppm)	Note
280	Pre-industrial levels
421	Current levels (approx.)
1,000	ASHRAE recommendation for indoor air quality
5,000	US 8-hour occupational exposure limit
10,000	Cognitive impairment, Canada's long-term exposure limit
20,000-50,000	Headaches, drowsiness, poor concentration
>70,000	Suffocation, unconsciousness, potential death

Historical Hazards

Historically, miners referred to asphyxiating gases like CO₂ as "blackdamp." They used canaries as early warning systems for dangerous gas levels in mines. Accidents involving dry ice have also highlighted the risks of high CO₂ concentrations in poorly ventilated areas.^[63]^[64]

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References

where "part" here means per molecule[9]

A full list of references for this article are available at the Carbon dioxide Wikipedia page

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The Carbon Cycle's Cornerstone

💡 Dive in with Flashcard Learning! 💡

Understanding Carbon Dioxide 💨

⚛️ Chemical Identity

🌿 Biological Significance

🌡️ Atmospheric Role

Chemical and Physical Properties 🔬

📐 Molecular Structure

💧 Behavior in Aqueous Solution

📊 Key Physical Data

Biological Role and Processes 🌿

🌳 Photosynthesis and Carbon Fixation

📈 Plant Growth and Climate

🔄 Respiration and Decomposition

Sources of Carbon Dioxide 🏭

🔥 Anthropogenic Sources

🔬 Biological and Geological Processes

🍺 Industrial Byproducts

Commercial and Industrial Applications ⚙️

🚜 Agriculture and Fertilizers

🛢️ Enhanced Oil Recovery (EOR)

🥤 Food, Beverages, and Other Uses

Human Physiology and Respiration 🫁

🩸 Transport in Blood

⚖️ Regulation of Respiration and pH

Environmental Impact and Climate 🌍

🌡️ Greenhouse Gas Effect

🌊 Ocean Acidification

📈 Atmospheric Concentration Trends

Toxicity and Safety Thresholds ⚠️

😵 Health Effects of High Concentrations

🏠 Indoor Air Quality

⛏️ Historical Hazards

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📜 Important Notice

Dive in with Flashcard Learning!

Understanding Carbon Dioxide

Chemical Identity

Biological Significance

Atmospheric Role

Chemical and Physical Properties

Molecular Structure

Behavior in Aqueous Solution

Key Physical Data

Biological Role and Processes

Photosynthesis and Carbon Fixation

Plant Growth and Climate

Respiration and Decomposition

Sources of Carbon Dioxide

Anthropogenic Sources

Biological and Geological Processes

Industrial Byproducts

Commercial and Industrial Applications

Agriculture and Fertilizers

Enhanced Oil Recovery (EOR)

Food, Beverages, and Other Uses

Human Physiology and Respiration

Transport in Blood

Regulation of Respiration and pH

Environmental Impact and Climate

Greenhouse Gas Effect

Ocean Acidification

Atmospheric Concentration Trends

Toxicity and Safety Thresholds

Health Effects of High Concentrations

Indoor Air Quality

Historical Hazards

Teacher's Corner

True or False?

Test Your Knowledge!

Gamer's Corner

Discover other topics to study!

References

Feedback & Support

Disclaimer

Important Notice