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
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