is this an error or is it me??

[DDSguyLA]

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Gen Chem Problem 75 on Destroyer...
It says an unknown compound gets dissolved in water spontaneously and the water temp decreases.

The answer says the following is true.

Delta G < 0 (Which I undrestand since Delta G has to be neg for sponta)
Delta H > 0 (Which I undrestand since the temp is going down)
Delta S > 0 ( I DON'T GET THIS ONE )

If the temp of water goes down means it will boil at a higher temp.
When water boils it adds to the Delta S (entropy of the universe)
This compound makes the water boil HARDER meaning it is reversing the entropy... Correct???

In the answer it just says: Dissolving increases the amount of disorder (Delta S)


Thanks

 

[juicy]

I think the answer is referring to the entropy of the reaction (the system). When the substance (say a chunk of salt) dissolves in solution, it increases the number of ions, which increases the disorder of the system.

 

[Mstoothlady2012]

a compound is solid = very low entropy
a liquid = medium entropy
when we mix them together, the compound dissolves in water. Meaning there is no solid left, hence entropy increases overall

 

[scatmanjeffrey]

it says that the water temp decreases, meaning the reaction is endothermic. That means change in enthalpy (H) is positive. The other piece of info they gave you is that the reaction is spontaneous, so G is negative. Therefore, if you look at: G=H-TS, S has to be positive to make G negative. Hope this helps

 

[Hugh Mannity]

Entropy increases always as a solute is dissolved. Knowing G doesn't get you to that answer because to use S for spontaneity you need to know the temp (unless H is neg and S is pos then at all temp G is neg and rxn is spontaneous).

 

[DDSguyLA]

a compound is solid = very low entropy
a liquid = medium entropy
when we mix them together, the compound dissolves in water. Meaning there is no solid left, hence entropy increases overall

THANK YOU... i get it now

 

[arpitpatel86]

well there is a shortcut to this problem...look at the solution for problem 152....it says if your going solid---)liquid----) gas....transformation is positve for delta H and S

if your going from gas to liquid to solid they both are negative

since in this problem you are going solid to liquid
both are positive....

 

[wbloo]

As you boil, you are increasing the entropy (disorder).


Solids have the least amount of entropy - They are the most ordered, while liquids have more entropy and gases have the most amount of entropy. So as you go from solid to gas the entropy increases. Boiling thus, causes an increase in entropy.

Hope it helped!