Which factors promote the formation of solutions?

1 Answer
Mar 25, 2014

The major factor affecting solubility is intermolecular forces.

To form a solution we must:
1. Separate the particles of the solvent.
2. Separate the particles of the solute.
3. Mix the particles of solvent and solute.

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ΔHsoln=ΔH1+ΔH2+ΔH3

ΔH1 and ΔH2 are both positive because it requires energy to pull molecules away from each other against the intermolecular forces of attraction. ΔH3 is negative because intermolecular attractions are forming.

For the solution process to be favourable, ΔH3 should at least equal ΔH1+ΔH2.

If both solvent and solute are nonpolar, all the ΔH values are small. The major factor then is the increase in entropy (disorder) that occurs when a solution forms. This is a favourable process.

If both solvent and solute are polar, all the ΔH values are large but similar in size. The major factor again is the increase in entropy.

LIKE DISSOLVES LIKE.

If a nonpolar solute such as oil mixes with a polar solvent like water, ΔH1 is large and positive. This outweighs ΔH3. A solution does not form.