If delta G for the dissociation of Borax at 30 degrees C (higher than room temperature) is positive, why does it dissolve at room temperature?
3 answers
It gets the needed energy from somewhere. Do you suppose the solution gets colder?
Well, I know that the reaction is endothermic, because delta Hº is also positive. I just don't understand why delta G is positive, since the reaction seems to be spontaneous...
Here is a site that may be worth reading. Especially near the bottom where the discussion is on spontaneous versus non-spontaneous reactions.
http://www.800mainstreet.com/7/0007-003-free_energy.htm
The point is that non-spontaneous reactions (those with delta G = +) can take place if energy is added from elsewhere. My question was to suggest that the energy comes from the solvent. That is one reason why some solids dissolve and the solution gets cold; i.e., the energy to break the bonds comes from the solvent molecules and they get colder in the process. Of course, some molecule produce a lot of extra energy when the ions become hydrated; however, this is not always enough to break the bonds of the crystal and the energy comes from the solvent decreasing T.
http://www.800mainstreet.com/7/0007-003-free_energy.htm
The point is that non-spontaneous reactions (those with delta G = +) can take place if energy is added from elsewhere. My question was to suggest that the energy comes from the solvent. That is one reason why some solids dissolve and the solution gets cold; i.e., the energy to break the bonds comes from the solvent molecules and they get colder in the process. Of course, some molecule produce a lot of extra energy when the ions become hydrated; however, this is not always enough to break the bonds of the crystal and the energy comes from the solvent decreasing T.
7 answers