Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Endothermic reaction
Name: george t tuggle
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: 1999 


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



Replies:
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).

-topper


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.

-jschultz


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.

-topper


Oh, I forgot to mention....in 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!

-topper


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

-jschultz



Click here to return to the Chemistry Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory