Chemical Ice Pack/ Endothermic Quick Freeze

This demonstration mixes two solids which react endothermically, taking in enough heat to freeze a wet block of wood to the flask. The chemicals used for this reaction are barium hydroxide octahydrate [Ba(OH)2 8H2O] and ammonium nitrate [(NH4)(NO3)] , and when they react they take in heat energy (which is what freezes the water) and form water and dissolve each other.

[@mrtarpon]

Oh my god would the students shut up.

[@hararuray2793]

This is why I love chemistry!!!

[@turtlemanx15]

i wish you were my teacher. you're like the coolest guy. none of my science teachres before did coool experiments.

[@mrericsully]

I'm sorry to hear that, but thanks for the complement. Science is great because it can be visual and even hands on, but too many teachers don't take advantage of this- I personally cannot imagine doing it any other way.

[@mrericsully]

@shahidfurqan2003 Ammonium nitrate is somewhat easy to obtain although its purity might be questionable from some sources. Barium hydroxide on the other hand is not readily available.

[@mrericsully]

That is correct. There are not many solid-solid reactions that are easy to preform and few of them get cold or form a liquid/aqueous product.

[@mrericsully]

I'd use the Hess's Law formula. You'd also need the entropy (delta H) values for each of the reactants and products- I'd ave to look tose up form a table, I don't just know them. As far as the ratio of reactants you need a balanced reaction equation: Ba(OH)2 8H2O + 2 (NH4)(NO3) -> Ba(NO3)2 + 2 NH3 + 10 H2O. The molar ratio is 1:2 according to the way I have it written here. There are a few variations on this demonstration so you may want to check the reactants.

[@Envy987001]

I got a question. If you could theoretically compress water enough could you turn it into ice through force?

[@esteinapt9]

are there two chemicals you could use that would produce a similar effect that could be placed on the skin?

[@Polaf3456]

I have a question! If you freeze the solution of mixed water/ammonium nitrate, can you extract the ammonium nitrate from the solution?

[@bmwsux6]

Mr. sully. Would this also work on the cheap with sodium hydroxide [lye] and ammonium nitrate?

[@mrericsully]

No because sodium hydroxide is very exothermic [gives off heat] as it dissolves. Also you would need to add water in that situation because the water in the slurry here comes from the waters trapped in barium hydroxide. It is possible to notice the endothermic heat of solution of ammonium nitrate if you just dissolve it in water [this is often used in instant cold packs], but it will not get to the freezing point of water.

[@mrericsully]

@heavenly98 I'm not at school right now and so I don't recall which is which, but I use 16-18 grams of one and 32 of the other. You cold probably work it out with stoichiometry, or wait until I"m back at school and I will try to look it up.

[@matlilly8795]

How about the class shut up and learn? I would get demerits for going off on someone for talking during learning time.

[@mrericsully]

If you only dissolve it then yet, however why dissolve it in the first case if that is your goal (unless you are trying to do purification through crystallization). However, as I've pointed out in other comments in this particular demonstration I do a reaction that turns the ammonium nitrate into other things (mainly ammonia gas and barium nitrate) such that there is no ammonium nitrate left to recover. When I were to evaporate this solution I have barium hydroxide.

[@rami111511]

Could you please tell me how to calculate the amount of heat that the reaction needs?? and what is the ratio of the salts in this reaction?

[@jh.arturo]

you don’t need heat. it absorbs the heat from it’s environment when you mix it, making the things it absorbed heat from colder.

[@mrericsully]

@esteinapt9 If you are talking about just cooling the skin [like a chemical ice/cold pack] yes- in fact this reaction is used in some, but because of the toxicity of the Ba(OH)2 many times the (NH4)Cl and H2O are used [it has an endothermic heat of solution]. If you are talking about freezing that skin that is unsafe and could cause frostbite and although I know ways I wouldn't try them. If you are talking about direct application to the skin it would be doable, but is easier to make a pack.

[@mrericsully]

Not through freezing because it dissolves and freezing changes that freezing point, but the ammonium nitrate is still dissolved. There are ways to get it back out, but freezing is not one of them. Also, keep in mind that in this demonstration I do a reaction and so then the original material is consumed as a new products are formed, so it doesn't work all the more.

[@user-eq7xs6er3y]

How long does the mix stays cold ? and what happens if something heat the mix ? If they warm enough do they increase the pressure ? Thanks !

[@mrericsully]

I've never measured the temperature change over long periods of time. When I do successfully freeze the wooden block to the flask [sometimes it doesn't work] it will stay frozen for up to a half hour. A little bit of heat before the reaction speeds it up because it is endothermic, but the temperature change can be masked (or at least not colder than room temperature) if you warm it up too much. Warming it up after the reaction drives it towards completion, but doesn't do much otherwise. There is some gas evolved in this reaction, plus some gas in the flask to begin with, so you get a minor pressure increase, but nothing much more significant than just heating a closed flask does. I'm sure you could pop the stopper off, but I would be surprised if you could do much more.

[@user-eq7xs6er3y]

Thanks !!

[@igotswtrice4u]

@@mrericsully what are the byproducts after the reaction is complete?

[@mrericsully]

The quantity of ammonia is pretty low (the smell is not as strong as household [1%] ammonia cleaner), and I do stopper it before I pass the vessel around. Personally I'm more wary of the barium compounds, but I'm glad you are safety minded.

[@heavenly98]

may i know the amount of barium hydroxide and ammonium nitrate used?

[@shahidfurqan2003]

@heavnly 98 bro tell simly way which chemical used and, is is it available every ware in market. where is other usage of these chemical's

[@jakedx13]

whats that thing in the bottom left

[@mrericsully]

I could have, but ammonium nitrate with barium hydroxide is even more endothermic resulting in a greater [and longer lasting]] temperature change.

[@SteoftheSouth]

but hes just showing how 2 solids react to for liquid and freeze

[@ericbenavidez7182]

cool.

[@Obileo346]

just a thought, ammonia, which is dangerous, is being produced in this reaction. (that's the smell) you should have covered the flask with that stopper you have and not let the observers breathe it in.

[@leonardomalburg]

Does the reaction last 30 min?

[@mrericsully]

No, the reaction itself only last a couple of minutes, but the cooling enough to freeze water does last about 20-30 minutes.

[@leonardomalburg]

Yeah, sorry. I meant the cooling. That's perfect. Is there any way to make it last longer?

[@mrericsully]

Upping the quantities of reactants used would probably make it drag out longer. Also, maybe with an insulated container, but that depends on your desire for use. If the goal is to use it like an ice pack then an insulated container will also prevent "the cold from getting out". Beyond that there are several other variations on chemicals that can be used for this reaction. If I remember correctly, this combination is the next to coldest (and is decently toxic and expensive). There is one common combination that is slightly colder, but is more expensive and so I haven't done that one in my class before.

[@leonardomalburg]

Nice. Yeah, for you to understand what's my intention with that. I'm developing a cooling system for a RC Boat that i'm going to present in a Science fair. I should create something considering physics and something using chemistry.

[@mrericsully]

Try it, if you are using it as a heat sink it may or may not last as long as you need it to, but I think part of any science fair exhibit should show experimentation and trying (even if it doesn't work).

[@mrericsully]

@oxsweety18xo If I put water in the flask the reaction would seem less endothermic because it would also have to cool the water and if might not get cold enough to freeze the wood disk to the flask. Beyond that the reaction should still occur, but more of the ammonia gas that is released would dissolve in the extra water forming basic ammonium hydroxide. Also, it would ruin the fun of the rare/uncommon solid-solid reaction.

[@seppejoos9380]

What is UREA

[@bmwsux6]

seppe joos: CH4N2O or UREA is commonly found in urine.

[@seppejoos9380]

Ok thx found it in instand cold pack

[@wes.1528]

that's how dry ice packs are made right when you squish them together they become cold

[@mrericsully]

Kind of, instant cold packs usually just have one chemical inside of them that has a really endothermic heat of solution [ammonium nitrate and ammonium chloride are probably the most common], rather than using a reaction that has an endothermic heat of solution, especially since the barium hydroxide used here is so toxic. In a cold pack the water is usually in the part you pop and it mixes with one dry powder.

[@wes.1528]

ty

[@brownsrock2007]

haha my science teacher is awesome he took some potassium permanginate stuff and put some glycerin on it and we got purple fire and ended up lighting the trashcan on fire XD

[@darkstar3472]

Shhhhhhhh

[@mrericsully]

No it does not matter.

[@mrericsully]

Gas valve for Bunsen burners.

[@MrKicks2010]

bet this is highschool lol kids are so damn rude...