Making a Soda Slush
Most recent answer: 01/30/2015
- Rob (age 16)
Maine, USA
At 27°F, or -2.8°C, your soda can probably usually supercool. (See , .) That means it will get that cold but won't start to freeze. Twisting the cap and turning it upside down is likely to trigger the freezing, because the sudden reduction in pressure will trigger a lot of bubble formation, and those bubbles may help nucleate ice formation. Once the water starts to freeze, the formation of the ice releases "latent heat" that warms everything up. Starting at -2.8°C, it doesn't take much warming to get to 0°C. The freezing will stop just before that, because the various solutes (sugar,..) in the soda reduce its freezing point. Each gram of ice that forms releases enough heat to warm almost 30 grams of soda from -2.8°C up to 0°C. So you probably end up with about 3% of the soda in the form of ice, enough to make the whole thing slush.
Without supercooling, at -2.8°C your soda would freeze more solidly. It wouldn't all turn solid, because the sugar etc. that gets left out of the ice would make some very concentrated soda liquid with a freezing point of -2.8°C. You can figure out how big that effect is by taking your slush and leaving it in the freezer another few hours.
Mike W.
(published on 01/30/2015)