Ice Dam Help

[JohnnyD]

Originally Posted by Saltheart

Nope , you had it right Johnny D.

When we use either CaCl2 or NaCL to melt ice , its because it lowers the melting point of the water. There is virtually no contribution of an exothermic reaction at the very low levels it gets diluted to when you use a sprinkle of salt on an icy surface. yes , a spoon full in a small amount of water will raise the temp but for the use in melting ice , its all Phase diagram stuff , not exeothermic reaction. It actually will lower freezing point to -50 degrees at a 30 wt% solution but my guess is that at the concentrations we use , it might lower it 4 degrees or so.

The experiment to prove this using the video shown , would to be to put the reacted mixture that was raised to 50C inot a freezer. The freezing point of the water would be way low , maybe approaching -50 C at the concentration he used. Remember , in the freezer you are not taking the salt out. You are just taking heat out and even though all the heat of the reaction is gone , the water with the same salt in it still has that hugely lowered melting point.

To read more , search for "water/Calcium Chloride Phase Diagram.

Saltheart
MIT 77

So... Phil and I are both kind of right?

[PRBuzz]

Originally Posted by JohnnyD

So... Phil and I are both kind of right?

I like that...on a grand scale. I'm a single molecule scale guy!

If there is no water and its below freezing...each crystal/molecule CaCl2 on a molecular scale reacts with snow/ice to generate water based upon mini-exothermic reactions, e.g. ice melts. The thing cascades and makes more water which dissolves more CaCl2. The more water the more CaCl2 dissolved the lower the freezing point which causes more ice to melt.

[ecduzitgood]

I am confused, doesn't the solid calcium chloride generate heat untill it becomes liquid when exposed to water, either solid or liquid?

[PRBuzz]

Originally Posted by ecduzitgood

I am confused, doesn't the solid calcium chloride generate heat untill it becomes liquid when exposed to water, either solid or liquid?

Stay confused, sometimes we are better off that way!


Point 1: yes when adding solid/dry CaCl2 to water it will get warmer. The more CaCl2 the warmer it gets. The mixing is "exothermic".

Point 2: CaCl2 in water will lower the freezing point of that water. Again, up until 30% (w/v) that freezing point depression will eventually reach -50C. (Question: anyone know how cold -50C is? DAMN COLD!)

When determining the freezing point (or eutectic point) of a given solution of CaCl2 in water it doesn't matter at what temperature the CaCl2/water solution starts from, it is not a measure of how many BTU's to cool only at what point does the solution freeze. So if I take room temperature water, add CaCl2 depending upon how much CaCl2 it may get detectably warm (to the hands or see movie above), then cool it down to freezing it will still have the same measured freezing point whether I start from room temperature water, warm/hot water, or even cold water. The graph attached earlier takes 20 or more different solutions of CaCl2 in water and measures the freezing point of each solution.


Side point: Car antifreeze, ethylene glycol, if you mix 2 parts anitfreeze with 1 part water you get a solution that freezes at ~70C. Don't mix ratios in any greater as the freezing point rapidly rises!

[DZ]

Here is another solution. I take all my rigged eels which have been soaking in brine solution for years and place them on the ice dams. They slowly emit brine solution and keep my gutters free of ice. As long as it's cold the eels stay fresh - just don't leave them on your roof in the spring time.

DZ

[zacs]

Originally Posted by DZ

Here is another solution. I take all my rigged eels which have been soaking in brine solution for years and place them on the ice dams. They slowly emit brine solution and keep my gutters free of ice. As long as it's cold the eels stay fresh - just don't leave them on your roof in the spring time.

DZ

DZ- THAT IS CLASSIC