Why does a soda bottle fizz when opened?

A sealed soda bottle is pressurized with carbon dioxide dissolved in the liquid. Opening the cap suddenly drops the pressure inside, and the dissolved CO2 is no longer soluble at the new low pressure, so it rushes out of solution as bubbles — the fizz you hear.

Why does shaking a soda bottle make it fizz more?

Shaking introduces lots of tiny gas bubbles into the liquid. Each of those microbubbles acts as a nucleation site, an easy take-off point for dissolved CO2 to come out of solution. When you then open the cap, the pressure drops and the CO2 escapes through all those ready-made bubbles at once, producing a much more violent fizz.

Is shaking a soda a chemical change?

No, it is a physical change. Shaking only redistributes the existing CO2 between the gas headspace and the liquid, creating bubbles and nucleation sites. No new substances are formed, and the carbonic acid chemistry inside the drink does not change.

Does a warm soda fizz more than a cold soda?

Yes. Gas solubility decreases as temperature rises (Henry's law), so a warm bottle holds less CO2 in solution and has more gas in the headspace. When you open it, more CO2 comes out faster, and the fizz (and spray risk) is greater than for a cold bottle.

Does shaking soda and then waiting reduce the fizz?

Yes. If you shake a closed bottle and then let it rest for several minutes, the bubbles you created have time to rise to the top and rejoin the headspace, and CO2 redissolves into the now-still liquid. By the time you open the cap, the nucleation sites are gone, and the fizz is closer to a normal, unshaken bottle.

Why Does Shaking A Soda Bottle Make It Fizz Even More?

Table of Contents (click to expand)

Carbonation
The Fizz Factor
Why Does Shaking The Bottle Result In A Stronger Fizz?

A soda is bottled under high pressure with carbon dioxide dissolved in it. When you crack open the cap, the pressure drops and the CO₂ rushes out of solution, producing the fizz. Shaking the bottle first scatters tiny gas bubbles through the liquid — these act as nucleation sites where dissolved CO₂ can quickly come out of solution, so when you then open the bottle the gas escapes much faster and the fizz is more violent.

Soft drinks have intrigued me since I was a kid. At first, I was fascinated by their sweet taste, but as I grew up, I became more fascinated by something that precedes the act of gulping down the contents of the bottle: the “fizz”, which comes in the form of a fizzing sound every time a soft drink bottle is opened. Can’t we simply have a soft drink bottle that doesn’t announce its imminent opening?

Recommended Video for you:

Do Pepsi, Coke and Other Cold Drinks Contain Caffeine?

Carbonation

Soft drinks usually contain a considerable amount of carbonated water, artificial sweeteners, and flavors that make them taste so good. The drink contains dissolved carbon dioxide gas, so this process of adding carbon dioxide to the liquid is called carbonation.

As soon as carbon dioxide gas comes in contact with water, a small fraction of it reacts to form aqueous carbonic acid (H₂CO₃). Most of the dissolved CO₂ stays as plain dissolved gas, but the tiny amount of carbonic acid that does form gives the drink its tart, slightly biting flavor. The CO₂ bubbles also stimulate sour-taste receptors and trigeminal nerves on the tongue, which is the prickly sensation you get from a fresh soda. Strip those bubbles out and almost every soft drink tastes too sweet, bland, or ‘flat’, as many call it.

The Fizz Factor

Cola Fizz — Credits:Merydolla/Shutterstock

Now that you know that the fizz is caused by the dissolved carbon dioxide, let’s take a look at why there is fizz in the first place!

Carbon dioxide is not readily soluble in liquids at normal pressure; so in order to dissolve it into the drink, it is subjected to a high pressure and then pushed inside the can (or whatever container the drink comes in). For our purposes, let’s consider a bottle. As long as the bottle is closed, the insides of the bottle are at a uniform pressure, but as soon as the bottle is popped open, there is a drastic change in the air pressure between the inside and outside of the bottle and the gas molecules suddenly have access to a lot more space to occupy. The result of this pressure difference is the fizzzzz sound you hear when the bottle is uncapped; the trapped carbon dioxide molecules are escaping rapidly, so fast that you can hear it!

Why Does Shaking The Bottle Result In A Stronger Fizz?

You’ve surely noticed that when you shake a bottle before opening it, the fizz is stronger. Why does that happen?.

As mentioned earlier, a capped bottle is under a uniform pressure; in other words, the conditions inside a capped bottle are constant, as the molecules of carbon dioxide gas and liquid are at an equilibrium (due to a uniform pressure). The carbon dioxide molecules are held tightly in the clutches of the liquid. In order to break free, they need sufficient energy. And what is one way to gain that energy? Yes, you guessed it… by being shaken rapidly.

To start making a bubble, the energy required is pretty high, as the gas has to break through the liquid’s surface tension. However, once a small bubble is formed, it is easier (requires less energy) for the surrounding gas molecules to join it to form a bigger bubble and escape through. Shaking a bottle introduces a lot of small bubbles into the liquid. As you continue shaking the bottle, more and more energy is imparted to the gas molecules and more bubbles become attached to the bubbles that are already present, thus making the process of the gas escape even more rapid. The outcome?

More fizz!

fizz meme

Some of the most common phenomena that we observe in daily life depend on very basic laws of nature related to the equilibrium of various forces and pressures. The fizz of a soft drink is just one of those events that show how a slight difference in the surrounding conditions can unleash a truly fascinating spectacle!

Next time you’re holding a bottle of soda, eagerly awaiting its fizzy refreshment, why not give it a shake and see science in action?

References (click to expand)