|MadSci Network: Chemistry
Well, the fizzing behavior is driven by one thing: the soda (diet or regular) is super-saturated with carbon dioxide and wants to reach an equilibrium with the atmosphere after you've opened it. Anything you put into the soda will help the gas bubbles to escape faster because it give the carbon dioxide bubbles more surface area on which to form, so it will fizz more.
Try to think about it this way - you are a molecule of CO2. You and thousands of your friends are all crammed into your back yard (an over-saturated environment), surrounded by a chain-link fence (liquid surface). None of you individually can easily break through the fence (surface tension), though a few here and there go over or under the fence (diffusion). But you all want to get from your side of this chain-link fence to the other side where you will have more room to move around (drive to equilibrium).
Someone now throws a hoolahoop into the back yard - what happens? Everyone tries to grab onto it (aggregation). The large group of you (a bubble) is now strong enough to break through the fence (liquid surface) to freedom.
Odd analogy, I know, but the fizzing is really a physical reaction to the presence of the mint, than a chemical reaction.
Thanks for your question and I hope this description helps.
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