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Thermodynamics/ammonium hydroxide


QUESTION: I have searched the internet and I can't find the answer to my question. I want to know how much energy in kwh would be needed to decompose, separate ammonium hydroxide into water and ammonia gas. If I have a given solution that is 30% ammonia. How much energy to remove 29.99 of it from the water. This is not a homework question. I'm working on a balloon project and I want to know how much heat to add to a solution of ammonium hydroxide to get the ammonia gas out to add more lift or decrease if I remove heat. I thought about using compressors but they are to heavy.

ANSWER: Hi Emmanuel,

You need 30.5 Jules per mol of NH3 (17g) enegy input. You also need to raise the temperature of the solution to about 80C to get good evolution of ammonia gas. You would also need to dry the ammonia as water from the solution would reduce lift significantly. You also have the dead weight of the water to lift. Also ammonia gas is toxic, flammable and corrosive.

I hope this helps.

Best wishes

---------- FOLLOW-UP ----------

QUESTION: Yes it does thank you very much. But i don't really understand it seems to low 30.5 joules per mol. For example in a gallon of ammonium hydroxide which has a weight of 3000 plus grams if you divide the 17 by 3000 you get 176 times 30.5  = 5382 total joules which comes out to .0016666 kwh I think thats low for removal ammonia gas from a gallon of ammonium hyroxide, but I do appreciate you took the time to give me an answer. I have an other question if i mix ammonia gas with pure hydrogen to I get ammonium hydroxide becasue i remember reading some where that ammonium hydroxide is mainly nh4. I want to use ammonia gas ass a lifting gas use either water or more hydrogen to remove  lift with out letting the ammonia gas escape becasue the cost would be to much, getting ammonia gas every launch. But yes thank you very much for your assistant so far. Its just something I want to work on.

Hi Emmanuel,

Ammonium Hydroxide is essentially just ammonia gas dissolved in water. At ordinary temperatures and pressures it is about 30% ammonia and 70% water. Ammonia comes off this solution very easily even at room temperature that is why it takes very little heat to drive it off once you have heated the solution to 80C. The fact that it is only 30% ammonia means that if you start with 1kg of solution you will get 300g of gas =  17.6 mol = 395 l of gas. This will not be enough to lift the remaining 700g of water and its container!

Mixing ammonia gas NH3 with hydrogen gas H2 will just give a mixture of the two gases they do not react.

Using water to remove the gas is not possible due to the weight of water required (see above). A small light weight compressor is the way to go or cooling to liquify the ammonia.

I hope this helps.

Best wishes.


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Thermodynamics, chemistry, chemical reactions, kinetics, chemical reaction safety, dust explosion technology, static electricity. General science.


Over 40 years experience as a practicing thermochemist in industry. Head of the fire and explosion laboratory of a major European chemical company (Ciba-Geigy). Now retired.

Institute of Chemical Engineers. Royal Society of Chemistry.

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