In my science-fantasy world there is a creature that secretes a venom (called a cryovenom) whose proteins catalyze a spontaneous crystallization of the water inside the interstitial fluids and affected cells of the victim. The reaction is highly endothermic, so that the end result is that getting bitten by this creature gives you literal frostbite. Am I breaking any laws of thermodynamics here or is it plausible enough to suspend your disbelief?
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7$\begingroup$ How does this avoid an ice-nine scenario? If there's a catalytic endothermic pathway to freezing water at body temperature, why are the oceans not frozen over? $\endgroup$– addaonCommented May 3 at 19:46
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$\begingroup$ Idk, I suppose that's why I asked :) My vision is that the catalyst doesn't produce an infinitely self-sustaining run-away reaction but instead nucleates a relatively large volume of water into ice relative to the amount of catalyst. There is at least small precedent for this sort of thing where you can facilitate ice crystal formation purely geometrically, and a venom that basically forces the water molecules into orientation with each other so it's easy to freeze rather than supercool them is more what I was imagining. $\endgroup$– Chromatic RealmsCommented May 8 at 19:24
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2 Answers
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So here's a thing you may not be familiar with: heat of fusion.
Very loosely speaking, your liquid bits are liquid because the molecules that make them up have a certain amount of energy. In order for your liquid bits to become crunchy bits, they energy has to go somewhere. In a seeming paradox, the act of freezing someone solid all of a sudden has to shift quite a bit of energy out of a person and into the surrounding environment in quite a short period of time... that's quite an exothermic process from the point of view of the surroundings!
And that in turn presents a bit of an issue. How long will a little bit of ice on your body last, if the act of creating it has heated up its surroundings, conveniently by the same amount of energy required to thaw it out? Freezing a human is quite an awkward process, which tends to be quite slow, and involve either brief exposure to intensely cold substances (which can in fact suck a lot of heat out of a person, that heat of fusion, causing freezing to occur) or long term exposure to merely freezing environments that can get rid of all that energy eventually.
You can have strongly endothermic chemical reactions, but the key thing there is that they're not catalytic in the way you're hoping for... the reaction occurs, heat gets sucked in, then you run out of reactants and it stops. The small amount of venom that could be injected into a person can't really absorb enough heat to produce a noticable effect. Instant cold packs can sometimes cause cold injury, but they involve a relatively large quantity of material.
So, unless your universe is literally operating within the rule of cool, you're out of luck here.
(that said, a monster that produces victims whose clothes caught fire but somehow still died of deep frostbite does sound kinda awesome in a suitably soft-scifi setting...)
editted to add:
Having put a bit more thought into this, it seems slightly less implausible if instead of magically catalyzing ice formation, you have a toxic cocktail that does two things.
Firstly, there are real-world biological compounds called ice-nucleation proteins that are used by bacteria to attack plants, causing frost-damage that exposure more nutrients to the bacteria.
Secondly, you may just be able to handwave in some reaction between toxin components and some part of the victim's biochemistry where it is that reaction which is endothermic.
Between the two, maybe you can trigger localized third degree frostbite (content warning: some graphic images of frostbite damage on humans). You still have to do a lot of handwaving, because people are warm and you need to lose a lot of energy to freeze them, and if you squirt a load of venom into them it'll have its own unpleasant toxic effects even without this magical freezing, and if you damage a large amount of material of the target by chemically breaking it down then you're causing some nasty and potentially fatal necrosis anyway (see real world cytotoxins, eg. the effects of recluse spider bites... content warning, some more unpleasant photographs).
The cold in that case is incidental, and the more realistic your setting the less it will be noticed, but there's soft-scifi wiggle-room there and it avoids the catastrophic ice-nine scenario your original suggestion had, as addaon pointed out.
answered May 3 at 20:11
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$\begingroup$ Thank you for the edit! Yes ice-nucleation was more what I was imagining. I know flash-freezing requires a ton of heat to be redistributed, but I do also know there are some interesting cases in the world of biochemistry and molecular physics where ice crystals can be encouraged to form more easily through water molecule orientation rather than just sucking the heat out of them. That's more what I was thinking. $\endgroup$ Commented May 8 at 19:26
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Breaking laws of thermodynamics?
Yes. yes you are.
The reaction as described decreasing entropy, crystals are highly organized, as well as decreasing enthalpy, thermal absorption.
A similar reaction would be spontaneously forming high explosives from air.
