Latent heat of fusion for water question

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Discussion Overview

The discussion revolves around the calculations related to the latent heat of fusion for water, particularly in the context of supercooled water transitioning to ice. Participants explore the implications of their calculations and the physical principles involved in this phase change.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant expresses confusion over a calculated temperature of 79 degrees Celsius resulting from their use of the latent heat of fusion and specific heat of water, questioning the realism of this outcome.
  • Another participant challenges the calculation, suggesting that the initial result is incorrect and prompting further elaboration.
  • A participant acknowledges the error in their calculation, clarifying that the units were not properly accounted for and that their notation was unclear.
  • One participant points out that when supercooling liquid water, the only heat to consider is that which reduces the temperature below freezing, emphasizing the importance of the temperature difference in their calculations.
  • Another participant suggests using Hess's Law to analyze the heat exchanges involved in freezing and supercooling, indicating a potential method to understand the latent heat terms better.
  • Some participants share links to external resources that may provide additional context or information relevant to the topic.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the calculations or the approach to understanding the phase change of supercooled water. There are competing views on the correct interpretation of the calculations and the physical principles involved.

Contextual Notes

There are unresolved issues regarding the assumptions made in the calculations, particularly concerning the treatment of temperature changes and the application of latent heat in the context of supercooling.

soronemus
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Hello,

I am doing some research involving supercooled water flash freezing into ice.

I am doing some calculations and I think that I must be wrong judging by my result.

Using the latent heat of fusion of water, and the specific heat of water, I can calculate a temperature value which should be the amount that the water heats up due to the energy released by the exothermic reaction of water turning into ice. This value was 79 degrees Celsius. This seems very unrealistic to me... According to that the water would jump from freezing almost to boiling. Am I doing something wrong?

Calculations: (4.2J/gC)/(334J/g) = 1/0.0125C ~79C
(latent heat of fusion / specific heat)
 
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soronemus said:
(4.2J/gC)/(334J/g) = 1/0.0125C ~79C
You might try this again.
 
I guess I don't see what I did wrong. Would you elaborate?
 
soronemus said:
Would you elaborate?
4.21/334 = 79? Think about it a moment.
 
4.21/334 is not 79 you are correct, it is .0125. The problem is that I still have the C unit left in the denominator when everything else cancels. I would think that you would have to take the inverse of .0125 (79) to get the temperature unit into the numerator and get my answer. My notation on my original post was kind of bad.
 
Specific heat will be in J/gC for one thing. You are supercooling liquid water; the only heat you have to account for is that removed to reduce the temperature below the freezing point. The only temperature rise in the system is from the supercooled temperature to the freezing temperature. That temperature difference times specific heat divided by latent heat will give you the total mass of solid you can form.
 
I did use J/gC for specific heat. The operation you are proposing cancels all units and leaves you with a dimensionless number if i am looking at it correctly. Thank you for trying to help, I think we might be on different pages. I found something more geared towards what I'm looking for here. http://www.phy.mtu.edu/~cantrell/agu2009-PosterSzedlakV5.pdf
Would you suggest any other resources on the subject?
 
soronemus said:
Would you suggest any other resources on the subject?
Do a Hess's Law cycle, or pair of cycles in parallel, summing heats for equilibrium freezing, and comparing that sum to a supercooling cycle to see where you're losing/gaining a latent heat term to "boil" water.
 
soronemus said:
I did use J/gC for specific heat. The operation you are proposing cancels all units and leaves you with a dimensionless number if i am looking at it correctly. Thank you for trying to help, I think we might be on different pages. I found something more geared towards what I'm looking for here. http://www.phy.mtu.edu/~cantrell/agu2009-PosterSzedlakV5.pdf
Would you suggest any other resources on the subject?
Some of the water will become a solid, and some will remain as a liquid. The liquid water will have a temperature increase no more than to 0C as heat is released from the freezing part of water, which also ends up at 0C.

You can read this lab example to get the idea.
http://www.colorado.edu/MCEN/flowvis/galleries/2011/Team-1/Reports/Schollenberger_Scott.pdf
 

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