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Name: george t tuggle
Status: N/A
Age: N/A
Location: N/A
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Date: 1999 

Can I use Sodium Nitrate as an example of an endothermic reaction?

I'm a scientist, so it's my job to be picky.... ;-) You mean, "Can I use the solvation of sodium nitrate in water as an example of an endothermic reaction?"

As the Magic 8-Ball says, "My sources say yes." Atkins' Physical Chemistry (4th edition) says that the limiting enthalpy of solution at STP for NaNO3 is +20.4 kJ mol^-1....which is even more endothermic than the enthalpy of solution of NaCl (+3.9 kJ mol^-1).


From personal experience, potassium chloride works real well too. There's also a mixture of two salts that is so endothermic that it gets cold enough to freeze water. I'll see if I can find the recipe.


Joe, maybe you are thinking about the case where you mix crystals of barium hydroxide octahydrate [Ba(OH)_2 . 8H2O] with crystals of ammonium nitrate [NH_4 NO_3]. The reaction, which is endothermic, is

Ba(OH)_2 . 8H2O (s) + 2NH_4NO_3(s) -> 2NH3(g) +10H2O(l)+Ba(NO_3)_2(aq)

with DH = 170 kJ / mole. This experiment MUST be done with proper ventilation due to the evolution of ammonia. See chapter 6 of Ebbing's "General Chemistry" text for a description of this experiment.


Oh, I forgot to order to see this reaction freeze water, you mix the two crystalline substances together in a beaker or Erlenmeyer flask throughly, and then set the beaker/flask onto a puddle of water on a wooden board. In a couple of minutes, the flask and the board are frozen solidly together!


That's the one! And yes...we usually do this one in a big lecture hall too.


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