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Freezing


Nave

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Well yesterday in chem class my teacher mixed powders together and they began to mix into like a paste. However he doing this on a board with water under the beaker. When he lifted up the beaker the board was frozen to it and he measured the temp of the solution and it was -40 C..... I was really cool... Now i was wondering are there two chemicals or more that can mix together as liquids and freeze instantly... So as soon as you put the liquids together they are completly frozen?

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i've seen ammonium chloride and the octahydrate of barium hydroxide do this. basically, the barium hydroxide is very hydrated and it loses its water when shaken with the ammonium chloride, causing the dissolving of ammonium chloride and creating a suspension of barium hydroxide. this is an overall endothermic process.

 

think of precipitating reactions; thats a good way to get solids from liquids.

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ive done the barium hydroxide and ammonium chloride one also. Also adding ammonium nitrate to water gets pretty cold. TO make a really hot one that will boil u can add mg fillings to a solution of cuso4 and also what they use in mre's: finely powdered mg and iron + water.

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Also adding ammonium nitrate to water gets pretty cold.

Yeah ive done that b4. Got it down to -10 C. Still it doesnt freeze becasue its not just water. Its what they have in icepacks.

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ya, the chemical ice packs. Is the ammonium nitrate plus water auctualy a chemical reaction? Where i got the idea to do this one was in a science book and it said it is dissolving. Although my science teacher said it cant be just dissolving. Although, i cant see why a solid cant dissolve in water and have less energy so it pulls energy from the surroundings.

 

MAybe its forming a base in the "reaction", ill have to test the alkalinity.

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ammonium nitrate is actually slightly acidic in water.

 

remember the rule; breaking bonds absorbs energy while forming bonds releases energy. so, the energy holding NH4+ and NO3- together is greater than the combined energies holding NH4+ and OH- and H+ and NO3-. except wait, it's not NH4+ and OH-; you lose an H+ and get NH3(aq) and H2O, so:

energy of: (NH4+ + NO3-)+(NH3 + H+) > (H+ + OH-)+(H+ + NO3-)

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well you have to consider the energies. i think ammonium salts tend to have their endothermic properties because of the breaking of the H+ off the NH4+

Are all coordinate covalent bonds endothermic when they are broken?

 

~Scott

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"oh ok, i see - thats where the acidity comes from"

well the NH3 has basicity. the acidity is more from the NO3-

 

"Are all coordinate covalent bonds endothermic when they are broken?"

well, the breaking of any bond is endothermic. bond formation is exothermic. delta h depends on both the energy absorbed by breaking a bond and the energy released by forming another bond

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Freezing is basically removal of kinetic energy from molecules, isnt it ?

 

If thats true, then why cant we use magnetic force to freeze all the molecules of an object instantly ? That should freeze it instantly ?

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