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Chemistry 101


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#205 TooMuchFun

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Posted 11 October 2018 - 08:21 AM

It's won't crystallize into ice unless there's some transition energy provided, no. 
 

 

 

One does not "provide" energy to water to freeze it.  A cold environment does the opposite by removing kinetic molecular energy.

You are right but for the wrong reason.  The corollary question is "Does ice melt at 0 degrees Celsius?"

 

Both cannot happen at the same temperature.  In fact, neither one can.  The environment has to be warmer than 0 to melt ice and colder than 0 to freeze  water.  At precisely zero, there is perfect equilibrium, as in the triple  point.  This is overlooked by all chemistry classes and professors as they teach the zero mantra.



#206 GAHD

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Posted 11 October 2018 - 08:51 PM

One does not "provide" energy to water to freeze it.  A cold environment does the opposite by removing kinetic molecular energy.

You are right but for the wrong reason.  The corollary question is "Does ice melt at 0 degrees Celsius?"

 

Both cannot happen at the same temperature.  In fact, neither one can.  The environment has to be warmer than 0 to melt ice and colder than 0 to freeze  water.  At precisely zero, there is perfect equilibrium, as in the triple  point.  This is overlooked by all chemistry classes and professors as they teach the zero mantra.

Yeah.. yer wrong. It DOES take energy to transition away from liquid state, even from liquid to solid. I think you don't understand molecular lattices. :) For exactly different reasons than that the propane thing works it's magic, (really any compressed liquid -> decompressed gas transition) liquid -> solid takes a bit of energy to arrange and order itself. That's WHY you can super-cool pure fluids, they don't have the energy they need to move into a lattice shape. It's also one of the keys to Ice II and Ice III



#207 exchemist

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Posted 12 October 2018 - 01:41 AM

Yeah.. yer wrong. It DOES take energy to transition away from liquid state, even from liquid to solid. I think you don't understand molecular lattices. :) For exactly different reasons than that the propane thing works it's magic, (really any compressed liquid -> decompressed gas transition) liquid -> solid takes a bit of energy to arrange and order itself. That's WHY you can super-cool pure fluids, they don't have the energy they need to move into a lattice shape. It's also one of the keys to Ice II and Ice III

Yes: https://en.wikipedia...cleation_theory

 

This is for gas - liquid nucleation, but liquid - solid will follow similar principles: volume reduction in free energy versus   rise in free energy at the surface, where the lattice structure is incomplete. 


Edited by exchemist, 12 October 2018 - 02:48 AM.