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Recently, I bought an ice pack that contained Calcium Ammonium Nitrate, and realized that it really didn't get cold. I came to the conclusion that perhaps Urea is more effective, yet it is still puzzling to me that in a perfectly secure ice pack, it got to refrigerator water temperature.

I was thinking, perhaps purity of compound and nitrogen content (46% in Urea vs ~23% in CAN) could make a difference.

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  • $\begingroup$ at equilibrium? $\endgroup$
    – bonCodigo
    Jul 14, 2017 at 0:06
  • $\begingroup$ Welcome to Chemistry.se! It seems you have accidentally created multiple accounts, please visit this page to find out how to merge them. $\endgroup$
    – Martin - マーチン ♦
    Jul 14, 2017 at 11:08
  • $\begingroup$ Greetings Omar. It looks like you created a second account to ask a slightly different question. If you want to alter your question, you can simply edit the current one. Or, if my answer below didn't quite address what you were looking for, you could leave a comment below my answer and I will try to clarify. It looks like you might be particularly interested in whether the nitrogen concentration is responsible for the cooling? In this case, it's really coincidental that the two compounds both contain nitrogen. Again, feel free to leave a comment asking for any clarification you need. Cheers. $\endgroup$
    – airhuff
    Jul 14, 2017 at 15:21

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The endothermic process is just the dissolution of the calcium ammonium nitrate (CAN) or urea in water.

The most likely explanation for the lack of cooling when you used your pack is that over time, by getting partially squished at some point, or from defective manufacturing, some water leaked out so that the CAN or urea had already been partially/fully dissolved by the time you tried to use it.

These reagents are pretty stable and it is very unlikely that the nitrogen had changed form or that the system had been contaminated.

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