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APPLIED FIZZICS Field Notes – Edition #4
We have a ton to talk about after last week. Let's start with a recap of last week's quiz.
Quiz
Last Week's Quiz
From Field Notes #3: Last week, I asked what would happen if you left a bottle of Champagne in a hot car all day.
The answer is: the pressure inside the bottle increases for two different reasons.
The first reason is the one most people think of. As the bottle warms, the CO₂ molecules in the headspace move faster; and molecular speed is essentially the definition of temperature. And faster molecules hit the inside of the bottle in the headspace with greater frequency and each with greater force; and that is at the very heart of the definition of pressure. So, faster molecules means higher pressure.
But several readers pointed out something equally important. Mikey, in particular, noted that warming the Champagne also drives additional CO₂ out of solution and into the headspace. In other words, the gas above the liquid isn't just getting hotter—it also contains more gas molecules than it did before.
Both effects increase the pressure. The pressure doesn't rise simply because the gas gets hotter. It also rises because there is more gas in the headspace. And that extra CO₂ in the headspace comes at the expense of CO₂ that had been in solution in the Champagne.
Could a bottle of Champagne explode in a hot car? It absolutely could. While Champagne bottles are over-engineered to withstand several times the expected pressure of Champagne at serving temperatures, you could definitely get to bursting pressure in a hot car.
If you'd like to explore this idea further, this week's Physics Corner takes a closer look at equilibrium and shows how you can watch this process yourself using our molecular simulator.
While several readers were thinking about temperature, others challenged something else entirely.
In the last Field Notes, I mentioned a result from the scientific literature stating that roughly 80% of the CO₂ lost from Champagne escapes by molecular diffusion across the liquid surface, while only about 20% leaves through the visible bubbles.
Several of you immediately asked an excellent question.
How can there be an 80/20 "rule" if diffusion depends so strongly on the surface area of the glass?
That seemed like a fair question.
So we went back to the original research.
It turns out that the famous 80/20 measurement wasn't performed using every type of Champagne glass. It was measured using one particular glass geometry—a traditional flute.
That immediately raised another question.
What happens if we change the shape of the glass?
At first, I thought this would be a quick calculation.
It wasn't.
One page of notes became several pages of mathematics, and before long I realized I was writing something that didn't really belong in our Field Notes. Rather than trying to squeeze equations into an email, I've started something new: Applied Fizzics Research Notes.
The first Research Note asks a simple question:
How does the geometry of a Champagne glass affect CO₂ loss?
As a first step, I modeled a traditional flute and a coupe as simple cones of equal volume. Even this simplified model produces some surprising results.
Compared with the flute, the coupe has approximately:
- Four times the exposed liquid surface area.
- Half the wetted glass surface.
- One-quarter the distance that bubbles travel before reaching the surface.
Each of these changes affects CO₂ transport differently. A larger exposed surface tends to increase diffusive loss, while a smaller wetted area may reduce the number of active nucleation sites available for bubble formation. Shorter bubble paths introduce yet another competing effect, giving the bubbles less time to grow as they ascend.
The result is that the familiar "80/20 rule" can't be thought of as a universal law at all. It depends on the geometry of the glass itself.
Our simple model predicts that the exposed liquid surface of a coupe is roughly four times larger than that of a flute. That alone suggests diffusion may play a much larger role than it does in a traditional flute.
If you'd like to follow the mathematics, you can read Applied Fizzics Research Note #1, where I work through the geometry step by step.
Physics Corner
Physics Corner: A short aside that explores the science one layer deeper.
One common misconception in chemistry is that at equilibrium nothing is happening.
In reality, equilibrium is incredibly busy.
For an unopened bottle of cold Champagne in equilibrium, some CO₂ molecules are leaving the Champagne while others are returning to it. At equilibrium, these two rates balance each other.
Warm the bottle, however, and that balance shifts. More molecules escape from the liquid than return, increasing both the number of gas molecules in the headspace and the speed at which they're moving.
To make this easier to visualize, we wrote a simple molecular simulator that models CO₂ molecules moving between the liquid and the headspace. Watch this short video to see what happens after the system reaches equilibrium and the temperature is increased. Seeing the equilibrium shift is much more satisfying than simply reading about it.
You can explore the temperature dependence of CO₂ solubility on your own with the Applied Fizzics Molecular Simulator. Choose the third demo, Solubility of CO₂. Click the blue "+" button to add molecules, and use the Temperature slider to change the temperature.
Now let's move on to this week's quiz.
Quiz
This Week's Quiz
Question: A man and his wife decide to unwind at the end of a long day with a glass of Champagne. Each unbeknownst to the other, and trying to be helpful, opens a bottle of Champagne. Now there are two open bottles, so they return one bottle to the refrigerator, uncapped. They pour from the other bottle, so it is now about half full, and it also goes back in the fridge uncapped.
The next morning, which bottle will be the fizziest? That is, which will have lost the least CO₂?
- The full bottle
- The half full bottle
- Both will be equally carbonated
Here's a bonus question: Now let's assume that both bottles were capped before returning them to the fridge, with one of those spring-loaded caps that everyone uses.
The next morning, which capped bottle will be the fizziest?
- The full bottle
- The half full bottle
- Both will be equally carbonated
I'll reveal the answer—and the physics behind it—in the next Field Notes. As usual, the answer isn't quite as obvious as it first appears.
Until next time, stay curious.
President, Applied Fizzics
