Carbonated Drinks Carbonated drinks are everywhere. Their sparkling fizz is fun to drink. In US alone, over 13 BILLION gallons of Carbonated Drinks are consumed each year. Measured in cans, this means stacking cans of soft drinks until you reach all the way to the moon... and back... over 20 times!

Carbonation Air CO2 Liquid Gasses, like air, or CO2 can dissolve in liquids. This happens naturally when a gas comes in contact with a liquid. So, how does carbonation work? How do they get drinks so fizzy? Do you need complicated machinery, or can it be done easily at home? Zooming in on the boundary between the gas and the liquid... Air CO2 Liquid

Carbonation When there is an equal amount of gas dissolved in the liquid as there is pressure above the liquid, this balance is called equilibrium, and the carbonation process stops. Over time, the gases diffuse into the liquid naturally

Pressure MORE PRESSURE = MORE GAS This means more gas will enter the liquid by the time it finally reaches equilibrium. (the pressure above the liquid equals the gas dissolved in the liquid) When a gas is under more pressure, the gas is compressed. MORE PRESSURE = MORE GAS

Pressure Pressure Gas Dissolved Chemist William Henry (1775-1836) studied the relationship between pressure and the amount of gas dissolved in the liquid. Although we know that more pressure means more gas is dissolved in the liquid, Henry showed that they are directly related. Double the pressure, you double the gas in the liquid. Triple the pressure and you triple the gas dissolved. The gas dissolved doesn’t double INSTANTLY when you double the pressure, nor does it instantly cut in half when you drop the pressure in half. It does EVENTUALLY match once equilibrium is reached. Pressure Gas Dissolved

Partial Pressure Henry also did some investigation about mixed gasses. If you have a mixture of gas above a liquid, then a mixture of gasses will be dissolved into the liquid. Although this makes sense, what it means is important.

Partial Pressure For example It means that if you have a mixture of Air and Carbon Dioxide above the liquid, then there will be a mixture of Air and Carbon Dioxide dissolved in the liquid. So the gas dissolved in the liquid will only be PARTLY Carbon Dioxide.

Partial Pressure Instead, if the gas is ONLY Carbon Dioxide, then essentially the same amount of GAS will dissolve into the liquid. But in this case, instead of being only partly Carbon Dioxide, the gas will be COMPLETELY Carbon Dioxide. A drink with ONLY Carbon Dioxide will be fizzier than a drink with Air and Carbon Dioxide mixed together. Air reduces carbonation.

Carbonation 4 Gasses dissolve all by themselves into liquids The gas in the liquid eventually matches the pressure above the liquid Equilibrium 4

Pressure 9 Increasing the pressure increases the gas dissolved at equilibrium More fizzy 9

Partial Pressure Getting rid of the Air means there is ONLY Carbon Dioxide. More Fizzy 20

How It Gets Flat The gas dissolved in the drink is no longer held in by the pressure, and so it starts to escape Before a carbonated drink is opened, it is pressurized and carbonated. It is in equilibrium When the carbonated drink is opened, the pressure is released. The carbonated drink sees an imbalance. There is less pressure above the drink than gas dissolved in the drink PRESSURIZED CARBONATED NOT PRESSURIZED NO MORE BALANCE STILL CARBONATED In free air, there is nothing to keep the gas from floating away. The pressure is never able to build up, so the gas keeps escaping

How It Gets Flat The gas dissolved in the drink is no longer held in by the pressure, and so it starts to escape NOT PRESSURIZED FLAT NOT CARBONATED In free air, there is nothing to keep the gas from floating away. The pressure is never able to build up, so the gas keeps escaping

Flat with Lid When you put a lid back on your carbonated drink, it can still go a little flat. Just after you put the lid back on, there is no pressure. Carbon Dioxide is always seeking a balance, so gas starts to escape from the liquid. As the gas escapes the drink, the pressure builds up. In time, the pressure will match the carbonation and everything stops. It reaches equilibrium. STILL HAS SOME CARBONATION BUT NOW IT HAS LESS

Less Liquid, Flatter Drink When you have a lid on a drink that is nearly empty, the drink will end up much flatter than a full bottle. Carbon Dioxide will escape from the drink and build up the pressure until there is equilibrium. There is much more room, so more gas escapes before any pressure can build up LOW PRESSURE NO PRESSURE BALANCE The pressure and the carbonation will balance, but both will be low. HIGH CARBONATION LOW CARBONATION

Shaking The Carbon Dioxide will naturally seek a balance, or equilibrium. This happens gradually over time The process can take days or minutes, depending on how easy it is for the Carbon Dioxide to reach the liquid CAN NOT REACH THE DRINK CAN REACH THE DRINK In a simple container, it can take a long time to wait for it to carbonate itself. Only a few molecules have access to the liquid at a time The other molecules can’t reach the liquid, and will not be able to until the other molecules make it into the drink. All the molecules need to line up and take turns entering the drink

Shaking The more entrances into the liquid there are, the faster the Carbon Dioxide can enter the liquid. That way they don’t all need to line up and take a turn. This can be done by SHAKING the drink. ALL MOLECULES CAN REACH THE DRINK Shaking makes tiny bubbles that are mixed into the liquid. This means all of the molecules are near the liquid

Shaking With all of the tiny bubbles of Carbon Dioxide able to reach the drink, the carbonation happens much faster

Temperature Pressure Gas Dissolved Temperature Doubling the pressure doubles the gas dissolved at equilibrium. But Temperature also has an effect on the amount of Gas dissolved Doubling the pressure STILL doubles the gas But the ratio is changed by the temperature Temperature defines WHERE the equilibrium point will be! A WARMER liquid will dissolve LESS gas A COLDER liquid will dissolve MORE gas Pressure Gas Dissolved Temperature

Temperature The best liquid for carbonating is ice-cold liquid. It will be the most carbonated. Tap-water and juices made with tap water will not carbonate as well as ice-cold liquid, but they will still do okay. Room-temperature liquids are even less effective at being carbonated. Naturally, hot or boiling liquids essentially can not be carbonated.

Foaming When you shake a carbonated drink and give it to a friend, the drink sprays everywhere. What is going on? The pressure of the bottle presses in on the tiny bubbles and keeps them small When the bottle is opened, the pressure is released. The tiny bubbles expand. The low pressure also encourages gas to escape from the liquid into the bubbles. This makes them even bigger. The bigger bubbles rise easily and rapidly to the surface, foaming and spraying with great force. After shaking the drink, tiny and sometimes invisible bubbles remain. It takes a very long time for those bubbles to disappear. They don’t have enough floating power. The thickness of the liquid, friction against the bottle wall, and other things prevent the weak small bubbles from floating.

Carbonation Carbonation can be lots of FUN! It’s easy to understand when you remember: Carbon Dioxide is always trying to reach Equilibrium – a balance between pressure and carbonation Air reduces carbonation Shaking makes tiny bubbles that let all of the Carbon Dioxide reach the liquid at once Cold Temperatures improve carbonation