Difference Between Carbon Dioxide and Carbon Monoxide

Main Difference – Carbon Dioxide vs Carbon Monoxide

Gas is one of the three major states in which all matter can exist. The other two types are solids and liquids. Gases have unique properties that solids and liquids do not have. Gas molecules are very small and there are very few interactions between gas molecules. Various elements and molecules exist as gases at room temperature. Carbon dioxide and carbon monoxide are such two gases. The main difference between carbon dioxide and carbon monoxide is that carbon dioxide is composed of two oxygen atoms along with a carbon atom whereas carbon monoxide is composed of one oxygen atom along with a carbon atom.

Key Areas Covered

1. What is Carbon Dioxide
      – Definition, Structure, Properties, Applications
2. What is Carbon Monoxide
      – Definition, Structure, Properties, Applications
3. What is the Difference Between Carbon Dioxide and Carbon Monoxide
      – Comparison of Key Differences

Key Terms: Carbon, Carbonic Acid, Carbon Dioxide, Carbon Monoxide, Dipole, Double Bond, Molar Mass, Molecular Formula, Oxygen, Photosynthesis, Triple Bond

What is Carbon Dioxide

Carbon dioxide is a gas at room temperature which has the molecular formula CO₂. This gas is very common as it is released during the respiration of living organisms. It is also a major component in the photosynthesis process of autotrophs.

The molecular mass of carbon dioxide molecule is about 44 g/mol. It is a colorless and odorless gas. The molecular shape of carbon dioxide is linear. The two oxygen atoms are attached to the carbon atom by its two sides with covalent double bonds. The length of one C=O bond is about 116.3 pm. The molecule is symmetrical. Therefore, it is not a dipole. (A dipole is any molecule having partial electrical charges on atoms due to the type of bonding they have in that molecule). 

Figure 01: The 3D stick and ball structure of Carbon Dioxide molecule. The carbon atom is shown in black color while the two oxygen atoms are in red color.

Carbon dioxide is well dissolved in water forming carbonic acid (H₂CO₃). But carbonic acid is a weak acid in aqueous solution; thus, it is partially dissociated into its ions. Therefore, there is an equilibrium between gaseous carbon dioxide and carbonic acid in water.

Figure 02: Atmospheric Carbon Dioxide can be dissolved in water.

It has been found that the content of carbon dioxide in the atmosphere is about 0.03% and it is increasing rapidly. This increase is mainly due to fossil fuel burning and deforestation. One of the major products of fossil fuel burning is carbon dioxide. Most of the atmospheric carbon dioxide is absorbed by the forests. In other words, carbon dioxide is utilized by trees for their photosynthesis process. But with deforestation, the amount of carbon dioxide taken up by flora is reduced. As a result, the percentage of carbon dioxide in the atmosphere goes up.

However, the increased amounts of carbon dioxide in the atmosphere is unfavorable because carbon dioxide is a greenhouse gas. Greenhouse gases are able to absorb and emit infrared radiation. This causes the rapid increase of global warming.

What is Carbon Monoxide

Carbon monoxide is a gas at room temperature, with the molecular formula CO. It is composed of only one carbon atom and one oxygen atom. Hence the structure is essentially linear. The oxygen atom is bonded to the carbon atom covalently. But unlike in carbon dioxide, carbon monoxide has a triple bond between carbon and oxygen. The triple bond is composed of a double bond and a coordination bond. After the formation of the double bond, there are two lone electron pairs on oxygen atom. One of these lone pairs is donated to the carbon atom in order to form a stable molecule. Otherwise, the carbon atom does not obey the octet rule and the two lone pairs repel each other, resulting in an unstable molecule.

Figure 03: The stick and ball structure of Carbon Dioxide. The carbon atom is in black color while the oxygen atom is in red color.

The bond length between carbon and oxygen is about 112.8 pm; this is less than that of carbon dioxide since carbon dioxide has a double bond between carbon and oxygen whereas carbon monoxide has a triple bond between carbon and oxygen.   The triple bond attaches the two atoms tightly than a double bond, therefore, the bond length is reduced.

Since oxygen atom is more electronegative than carbon, there is a slight dipole moment in the carbon monoxide molecule. However, it is not a strong dipole since there is a coordination bond that donates electrons to the carbon (the dipole results in a partial positive charge on the carbon atom and the electrons donated by oxygen can neutralize some amount of this charge).

There is a very little amount of carbon monoxide in the atmosphere. Carbon monoxide is considered as a toxic gas. This is because it can bind with hemoglobin in our blood (where oxygen molecules bind) and block the transportation of oxygen to body cells. Therefore, the body cells do not get enough oxygen that possibly causes the death of those cells.

Carbon monoxide is a byproduct of incomplete combustion of fossil fuels. When a high amount of carbon monoxide is present in the dry air, it is considered as polluted air.

When carbon dioxide is passed through heated charcoal (carbon), carbon monoxide is produced. Carbon Monoxide act as a reducing agent by oxidizing into Carbon Dioxide. The oxidation state of carbon in carbon monoxide is +2 and it is oxidized to +4 state in carbon dioxide. Apart from that, carbon monoxide can be used to isolate copper metal (Cu) from CuO (copper oxide). The reaction is given below.

CuO_(s)    +    CO_(g)            →         Cu_(s)     +     CO_2(g)

A major reaction of carbon monoxide is the reaction with transition metals. This feature is used to obtain pure transition metal elements out of their compounds. Ex: Purification of Nickel

Difference Between Carbon Dioxide and Carbon Monoxide

Definition

Carbon Dioxide: Carbon dioxide is a gas at room temperature which has the molecular formula CO₂.

Carbon Monoxide: Carbon Monoxide is a gas at room temperature, with the molecular formula CO.

Composition

Carbon Dioxide: Carbon dioxide is composed of a carbon atom bonded to two oxygen atoms.

Carbon Monoxide: Carbon monoxide is composed of a carbon atom bonded to one oxygen atom.

Molar Mass

Carbon Dioxide: The molar mass of carbon dioxide is about 44 g/mol.

Carbon Monoxide: The molar mass of carbon monoxide is about 28 g/mol.

Carbon-oxygen Bond Length

Carbon Dioxide: The bond length between carbon and oxygen is about 116.3 pm in carbon dioxide.

Carbon Monoxide: The bond length between carbon and oxygen is about 112.8 pm carbon monoxide.

Bonding

Carbon Dioxide: There is a covalent double bond between carbon and oxygen in Carbon dioxide.

Carbon Monoxide: There is a covalent double bond and a coordination bond (altogether a triple bond) between carbon and oxygen in Carbon monoxide.

Formation

Carbon Dioxide: Carbon dioxide is produced by the complete combustion of fossil fuels.

Carbon Monoxide: Carbon monoxide is produced by the incomplete combustion of fossil fuels.

Chemical Reactions

Carbon Dioxide: Carbon dioxide cannot undergo oxidation reactions.

Carbon Monoxide: Carbon monoxide can undergo oxidation reactions.

Conclusion

Although carbon dioxide is considered as a useful gas for the environment, too much of it is not favorable since it causes global warming. Carbon monoxide is considered as a toxic gas and inhalation of carbon monoxide cause the death of cells due to the inhibition of oxygen transportation in blood. However, the two gases are present in trace amounts in the atmosphere and the percentage of these gases are increasing rapidly due to human activities. The main difference between carbon dioxide and carbon monoxide is their structure and composition.

References:

1. “Carbon Monoxide.” Carbon Monoxide – Molecule of the Month. N.p., n.d. Web. Available here. 12 July 2017. 
2. “Carbon Dioxide.” ScienceDaily. ScienceDaily, n.d. Web. Available here. 12 July 2017. 

Image Courtesy:

1.”Carbon dioxide 3D ball” By Jynto (talk) – Own workThis chemical image was created with Discovery Studio Visualizer (CC0) via Commons Wikimedia
2. “Carbon-monoxide-3D-balls” By Benjah-bmm27 – Own work (Public Domain) via Commons Wikimedia