Is CO2 Lighter Than Air or Heavy? In other words: Explanation

Under standard conditions, carbon dioxide is an acidic, nonflammable, colourless gas. When compared to the other two most common gases, it ranks third in abundance in Earth’s atmosphere. It is created when two oxygen atoms make a double covalent connection with a single carbon atom.

When released into the atmosphere, it acts as a greenhouse gas, keeping the planet at a constant temperature. Forest fires, volcanic eruptions, carbonated rocks, etc. are all natural sources of carbon dioxide. Also, it’s what most creatures produce when they breathe out.

Lots of you may be wondering if CO2 is heavier than air. This article serves as my response.

So, is carbon dioxide heavier than air? The answer is yes, carbon dioxide (CO2) has a greater density than air. Carbon dioxide molecules have only three atoms total, including two oxygen and one carbon. When all of these atoms are added together, the total atomic mass is 44, making CO2’s molecular mass 44, while air’s molecular mass is roughly 29. In addition, the density of carbon dioxide is 1.61 Kg/m3, while the density of air is just 1.22 Kg/m3. As a result, carbon dioxide is significantly denser than air.

Let’s take a deeper dive into the notion of the CO2 molecule to see what makes it so dense and heavy.

The question is why carbon dioxide has a higher specific gravity than oxygen.

To put it simply, several gases combine to make up the air we breathe. Nitrogen and oxygen, making up 78.08 and 20.95 percent of air, respectively, are the air’s primary components. Less than 1 percent of the air is made up of the other gases, such as carbon dioxide, methane, argon, etc.

About 0.04 percent of the air is carbon dioxide. It contains two oxygen and one carbon atoms. Carbon has an atomic mass of 12, while oxygen has a mass of 16.

Thus, 12 + 2 x 16 = 44 is the correct answer for CO2’s molecular mass.

However, air is not just one gas but a combination of many, with nitrogen and oxygen making up over 80% of the mix (almost 20 percent ). Nitrogen has an atomic mass of 14, while oxygen has a mass of 16.

Using the percentages of nitrogen and oxygen in the air, we may determine its average molecular mass.

A mixture of 80% nitrogen and 20% oxygen equals (80/100). N2 Plus (20/100) O2

By summing the masses of nitrogen and oxygen atoms

0.8 (2 X 14) + 0.2 (2 X 16) = 0.8 X 28 + 0.2 X 32

= 22.4 + 6.4

= 28.8

Accordingly, air has a lower average molecular mass than carbon dioxide. It should be noted that the total density of carbon dioxide is 1.61 Kg/m3, while the density of air is only 1.22 Kg/m3. This provides further evidence that carbon dioxide (CO2) has a density greater than that of air.

Carbon dioxide (CO2): Does it Float or Sink?

At the same temperature and pressure, pure carbon dioxide sinks in the air because it is denser than air.

However, the majority of atmospheric carbon dioxide is produced by natural processes like volcanic eruptions and the combustion of fossil fuels. As a result of these exothermic reactions, the carbon dioxide that is produced also heats up to a high temperature, decreasing its density and propelling it to the upper atmosphere.

Here, it’s important to realise that air is not composed of layers, with the densest and heaviest gases at the bottom and the least dense and lightest gases at the top. There would be no oxygen to breathe if this were the case.

Despite appearances, air is not a single gas but rather a complex combination of gases held together by the pressures and temperatures of the atmosphere and the kinetic energies of individual gas molecules.

As molecules continually collide with one another, neither the heavier nor the lighter are allowed to sink or rise to the top. Therefore, the air does not experience stratification of distinct gases.

However, in a fully undisturbed environment with stationary molecules, pure concentrated carbon dioxide will undoubtedly sink. However, this is an artificial state that cannot be found in the natural world.

See CO2 Lewis Structure, Geometry, Hybridization for more on the bonding in carbon dioxide.

Does CO2 Weigh More Than Oxygen?

True, at constant temperature and pressure, pure carbon dioxide is denser than pure oxygen. Comparing O2 with CO2, the former has a molecular mass of 32 and the latter of 44.

One more thing: oxygen has a density of 1.36, while carbon dioxide is 1.62. That’s why CO2 is denser and heavier than air.

An actual bottle of wine demonstrates this phenomenon. You probably know that various liquids are fermented in the presence of oxygen to produce carbon dioxide during the winemaking process.

Therefore, the carbon dioxide produced by the wine forms a layer above it when the bottles are packed, preventing the air oxygen from interacting with the wine.

This separation of the two gases aids in wine preservation because oxygen would otherwise react with the wine, destroying its flavour.

If carbon dioxide is heavier than air, how does it rise into the atmosphere?

Stratification of gases does not take place in air, as was discussed before. Because of the constant velocity of the gas molecules, they are constantly bumping into each other and blending together.

Due to frequent collisions and motions, gas molecules’ trajectories change so rapidly that gravitational forces can barely affect them in their natural environment.

Because of this, it is impossible for carbon dioxide molecules to settle to the ground in the atmosphere once they are released into the atmosphere as a byproduct of any process. This is the same concept as gas diffusion.

Diffusion is the process by which one can detect an odour from a distance, such as cigarette smoke when standing some distance from a smoker, a person’s signature scent upon meeting them for the first time, or the aroma of delicious cuisine when passing a restaurant.

How Dense Is Carbon Dioxide Compared to Air?

This table shows the relative densities of the various airborne gases.

GasDensity(in Kg/m3)
Carbon dioxide1.61
Water vapor0.76

To what extent does CO2 ever float in the air?

You probably did the candle experiment where you lined up three candles of varying heights and lighted them all at once back in elementary school. After that, a glass is placed over the candles and it is seen which one goes out first. In other words, what did you think would happen?

Because carbon dioxide is heavier than air, most of you probably think the shortest candle will go out first. Here, the shortest candle is the one to go out. Why?

As was said before, carbon dioxide is denser than air at standard temperatures.

Density of a gas, however, is highly dependent on both its temperature and pressure. As temperature rises, a gas’s density falls, and vice versa. A gas’s density increases as its pressure rises since these two variables are directly related to one another.

The hot carbon dioxide released by the burning candles rises to the top of the candle experiment because it is less dense than the chilly air around it. Once all the air in the glass container has been used up, the shortest candles will be the ones to go out.

Carbon dioxide has the same density as air when heated to 140 °C at 1 atm pressure. At similar pressures, the density of CO2 is about identical to that of air at ambient temperature (approximately 80 atm).

Questions and Answers (FAQs)

Is it true that carbon dioxide is lighter than water?

To determine the answer, we must first determine the molecular weight of water.

Two hydrogen and one oxygen make up water. Hydrogen has an atomic weight of 1, while oxygen’s is 16.

Since we are concerned with molecular weight, let’s consider water.

H2O = 2 (1) + 16 = 18

It has been shown that carbon dioxide has a molecular weight of 44, making it heavier than water.

Water vapour has a density of around 0.76 Kg/m3 in the gas phase, while carbon dioxide has a density of about 1.61 Kg/m3. This demonstrates that CO2 is heavier and denser than water.

Is it true that liquid carbon dioxide has a lower density than its solid counterpart?

To melt or freeze carbon dioxide, a very specific range of temperatures and pressures is needed.

To put this into perspective, the theoretical freezing point of carbon dioxide is 1 atmosphere of pressure and 78.5 degrees Celsius, but the transition from gaseous to liquid phase occurs at 56 atmospheres of pressure and 20 degrees Celsius.

Dry ice, or solid carbon dioxide, has a density of 1562 Kg/m3, while liquid CO2 has a density of 770 Kg/m3, demonstrating that the solid state of carbon dioxide is denser.

When compared to nitrogen, is carbon dioxide heavier?

Nitrogen has an atomic mass of 14 (correct). Nitrogen has a molecular mass of 28, while carbon dioxide has a molecular mass of 44 since it is found in the atmosphere as N2 molecules. So, it stands to reason that CO2 would be denser than N2.

Carbon dioxide is heavier and denser than nitrogen, as seen by its lower density (1.19 Kg/m3) compared to nitrogen’s (1.6 Kg/m3).

Which gas has the greatest density, exactly?

The density of radon is 9.40 Kg/m3, and its atomic mass is 222 amu, as seen in the table. Radon is the most dense gas because of this.

See for yourself how CO2 is heavier than air and how it sinks to the bottom of the bottle in the entertaining movie below.


Because CO2 has a molecular mass of 44 and air has a molecular mass of about 29, carbon dioxide is denser in the atmosphere. The density of carbon dioxide is 1.61, while the density of the air we breathe is only 1.22.

When things are just right, carbon dioxide (CO2) should dissipate into the atmosphere. However, air is made up of a rather uniform combination of gases, and the constant motion and collision of gas molecules prevents stratification from occurring in the atmosphere.

At 80 atmospheres, the density of carbon dioxide is very close to that of air at ambient temperature. To add insult to injury, at 140 °C and 1 atm, carbon dioxide is less dense than air.

Carbon dioxide weighs more than all other atmospheric gases combined. However, argon is the heaviest gas in the universe.

Enjoy Your Reading!

Read more: Understanding the Lewis Structure, Geometry, Hybridization, and Polarity of CH2Br2

Misha Khatri
Misha Khatri is an emeritus professor in the University of Notre Dame's Department of Chemistry and Biochemistry. He graduated from Northern Illinois University with a BSc in Chemistry and Mathematics and a PhD in Physical Analytical Chemistry from the University of Utah.


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