Nave Posted May 17, 2005 Posted May 17, 2005 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?
budullewraagh Posted May 17, 2005 Posted May 17, 2005 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.
H2SO4 Posted May 17, 2005 Posted May 17, 2005 Ive heard of chemicals that when you mix them together they begin to biol at room temperature.
Nave Posted May 17, 2005 Author Posted May 17, 2005 yeah in a vacum pump... however the pump wasnt good enough to freeze the water after it boiled.
akcapr Posted May 18, 2005 Posted May 18, 2005 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.
Nave Posted May 18, 2005 Author Posted May 18, 2005 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.
H2SO4 Posted May 18, 2005 Posted May 18, 2005 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.
budullewraagh Posted May 18, 2005 Posted May 18, 2005 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-)
akcapr Posted May 18, 2005 Posted May 18, 2005 so the stronger the bond of the soluable (ionic) compound, the colder the dissolution will be in a solvent
budullewraagh Posted May 18, 2005 Posted May 18, 2005 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+
akcapr Posted May 18, 2005 Posted May 18, 2005 wait im lost. so wat exactly happens wen AN dissolves in water?
H2SO4 Posted May 19, 2005 Posted May 19, 2005 I never knew that rule "breaking bonds absorbs energy, making bonds realeases energy".
akcapr Posted May 19, 2005 Posted May 19, 2005 so when AN dissolves u get NH3+ and NO3-. what does the h+ do?
BenSon Posted May 20, 2005 Posted May 20, 2005 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
budullewraagh Posted May 20, 2005 Posted May 20, 2005 "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
BenSon Posted May 20, 2005 Posted May 20, 2005 Got ya so once the CCB is broken it depends on what the new product formed is to tell is the reaction will be endo or exothermic. ~Scott
Deviation Posted May 20, 2005 Posted May 20, 2005 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 ?
budullewraagh Posted May 20, 2005 Posted May 20, 2005 well, when things freeze, bonds are formed as a lattice structure is achieved. you cant remove all the energy in something; absolute zero is impossible to achieve
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