Hello

Can anyone help me in understanding why non polar solutes dissolve in non polar solvents

I know like dissolves like thumb rule but how can we explain it? I know polar dissolve polar coz of the electric forces of attraction but i can't understand why non polar would dissolve a non polar

Question

Hello

Can anyone help me in understanding why non polar solutes dissolve in non polar solvents

I know like dissolves like thumb rule but how can we explain it? I know polar dissolve polar coz of the electric forces of attraction but i can't understand why non polar would dissolve a non polar

sinbearciante · Answer

Using the 2nd law of thermodynamics, we know that the entropy of the system wants to increase, and since there are no polar factors, the two can mix. By doing this, entropy increases.

anonymous · Answer

like dissolves like!

anonymous · Answer

But what about when a non polar solute is dissolved in polar solvent? Why non polar dissolve in non polar solvens better?

anonymous · Answer

Sin is correct.  Dissolution generally occurs because it increases entropy, mostly of the solvent.  Enthapic factors, such as the change in energy of the interactions, usually just help or hinder that a bit, and cause the solubility to be higher or lower at a given temperature.

For example, if you dissolve a polar solute in a nonpolar solvent, then the polar solute molecules lose the energy they have from their mutual dipole-dipole interaction and do NOT gain equivalent interactions with the solvent molecules that now surround them.  Similarly, if you dissolve a nonpolar solute in a polar solvent, some of the SOLVENT molecules now lose their dipole-dipole interactions with their neighbors, and these are not replaced by new interactions with the solute molecules that are now near them.  In both cases, you lose some favorable enthalpy, and this will reduce the solubility at a given temperature. 

On the other hand, if you dissolve a polar solute in a polar solvent, or a nonpolar solute in a nonpolar solvent, the interactions are generally unchanged: any solute molecule that loses a dipole-dipole interaction with a neighbor solute molecule gets it replaced with another dipole-interaction with a solvent molecule, and the same for the solvent molecules.  Nothing much changes.  That leaves the entropic driving force free to drive dissolution at a lower temperature.

anonymous · Answer

Thank you, that's a great explanation!