[bpeck8]

So a few days ago in class my professor mixed two solids together and it became cold, mushy/liquid and smelled bad.
here is the reaction: Ba(OH)2*8H2O(s) + 2NH4Cl(s) = BaCl2(aq) + 2NH3(g) + 10H2O(l)

What i am having problems with understanding are the terms entropy (not so much, i think i pretty much know this), enthalpy, and free energy relating to this reaction.

So for the entropy, this is what i think: this reaction changed from an ordered state to an disordered state. solid being ordered and gas,liquid being disordered. because this reaction became more disordered change in entropy (S) will have a positive sign.

For enthalpy: i am not quite sure. I think since the container that the reaction took place in became cold, the reaction absorbed heat? so the change in enthalpy (H) will have a positive sign, endothermic reaction. I think it was cold, i didnt get to feel it and i think i remember some in class saying the container was cold.

For free energy: according to this formula ( i dont know how to do the delta triangle symbol) G = H - TS. If H is positive and S is positive then free energy can have a sign of either positive or negative, this is with out doing any kind of calculations. So free energy is the energy left to do work?

[tamim83]

I have seen this demo several times.  Did your professor try to make the flask freeze to a wet piece of wood?  It gets that cold.   

So, if the surroundings gets colder, the reaction system is absorbing heat so  :delta:H is positive.  The entropy should also be positive, as you said, because you are creating a gas and liquid from two solids.  For  :delta:G to be negative,  :delta:S must be large (or the temperature needs to be high, but I bet your professor did this at room temperature ).  I know for a fact that this reaction is spontaneous, which implies that  :delta:G is negative.  So  the T :delta:S must be larger than the  :delta:H term.  This is an entropy driven reaction.  You can plug in some numbers to confirm this as well. 

Yes, the definition of the Gibbs free energy is that it is the "additional" work available after the reaction is complete. 

Hope this helps some. 

[bpeck8]

yes that cleared up alot of things, thank you very much. 

yeah the professor did this at room temperature while holding it.