Why do carbonated drinks lose their gas?

The little bubbles in sodas have been tickling the taste buds for quite a while. But yet, all the good things die out and the soda effervescence eventually flattens out. But by the way, do you know why?

gas loss

Know that the gas contained in soft drinks is at the origin of this exit of bubbles which fizz in our mouth. These carbon dioxide bubbles are infused into the liquid during production.

“It dissolves the same way sugar and salt can dissolve in water”, explains Mark Jones, chemical consultant and member of the American Chemical Society. Carbon dioxide, or CO2, is about 1.5 times heavier than air, so you might not expect to see CO2 rising in the air.

The escape of carbon dioxide

But initially, the soda is supersaturated with CO2. And according to the henry’s law, a principle of chemistry, the gas undergoes a pressure which encourages it to escape from the soda. This famous law of Henry stipulates that the quantity of a gas dissolved in a liquid is proportional to the pressure of this same gas in the environment of the liquid. This therefore influences the entry or exit of a gas in a liquid. When a soda is first opened, this pressurized carbon dioxide is released into the air. “This escaping gas causes the hiss that you expect from a new soda”explains Joe Glajch, analytical chemist and chemical consultant.

the carbon dioxide represents about 0.04% of the Earth’s atmosphere. When soda is left exposed to air, Henry’s Law suggests that the carbon dioxide in the soft drink naturally wants to reach the same concentration in the liquid as it does in the air. Thereby, “When a can or bottle of soda has been left open for a long time, the dissolved carbon dioxide inside eventually balances out with the carbon dioxide in the air outside”describes Mark Jones. “When the soda is less bubbly, we call it flat”he continues.

Flatten the soda

Moreover, shaking a can or bottle of soda will flatten the soda more quickly, since it helps the carbon dioxide it contains to escape. The shaking mixes the air in the empty space of the bottle or can with the rest of the liquid, resulting in bubbles. These bubbles can then serve as nucleation sites or points where atoms and molecules can cluster together. These nucleation sites bring tiny bubbles of carbon dioxide together. Larger ones can more easily escape the surface tension of the liquid, which is the energy required for liquid molecules to separate from each other.