chemistry 'like dissolves like' question

[jobberd]

I need an explanation for something that I can't quite grasp A polar solute will dissolve in a polar solvent because the solute will be surrounded by the same ionic forces that hold it together in the first place. A nonpolar solute will dissolve in a nonpolar solvent because the solut will be surrounded by the same Vanderwaal forces that held it together in the first place. However, these Vanderwaal forces are basically mimicking weak ionic forces, so why wouldn't a nonpolar solute dissolve in a polar solvent? The forces would be even stronger, wouldn't they? Please clarify

 

[jobberd]

^bump^

 

[webnewland]

I think like dissolves because different groups don't like to react with each other, therefore they don't come close and when they're far apart, van derwall's interaction is almost non-existent. Like water and a hydrophobic group for example, hydrophobic groups (non polar) clamp together (not dissolving) and only has vanderwall's interaction with each other.

hope this is helpful

 

[McPhreak]

Originally posted by: jobberd
I need an explanation for something that I can't quite grasp A polar solute will dissolve in a polar solvent because the solute will be surrounded by the same ionic forces that hold it together in the first place. A nonpolar solute will dissolve in a nonpolar solvent because the solut will be surrounded by the same Vanderwaal forces that held it together in the first place. However, these Vanderwaal forces are basically mimicking weak ionic forces, so why wouldn't a nonpolar solute dissolve in a polar solvent? The forces would be even stronger, wouldn't they? Please clarify

The forces would be greater I believe, but you are not taking a few points in consideration:

1) Van der Waals forces are EXTREMELY weak forces and your polar molecules will form stronger, more stable non-covalent bonds with other polar molecules

2) Entropy is a HUGE factor

In other words, you need to look at the COMPLETE picture

 

[jobberd]

Ah, so essentially, the likes stay together within their own forces? Yes, this would make sense, because a polar solute would not break apart due to the weaker Vanderwaal forces of the nonpolar solvent, nor would the nonpolar solute break apart since the polar solvents are already having strong forces between one another. Thank you very much

 

[tsunek]

also consider the tendency of water too exclude nonpolar compounds

 

[SmackdownHotel]

Nonpolar molecules are only weakly held together by Van der waals and other weak intermolecular forces. Little energy is used to separate them, and that's their downfall. A polar solvent like water has its molecules strongly (relative to a nonpolar solvent) attracted to each other through hydrogen bonding. If you were to dissolve a nonpolar substance, you'd have to disrupt some of these hydrogen bonds and not enough energy would be released from separating nonpolar substances to drive the process. It is energetically unfavorable. Instead, water (or any other polar substance) will form a rigid "cage" around the nonpolar substance where the water molecules are tightly bound to each other but fail to interact much with the nonpolar solute.