Energetics of the Solution Process. When a solute dissolves in a solvent… IMFs of solvent are...
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Transcript of Energetics of the Solution Process. When a solute dissolves in a solvent… IMFs of solvent are...
Energetics of the Solution Process
When a solute dissolves in a solvent…
IMFs of solvent are disrupted IMFs of solute are disrupted IMFs between solute-solvent are created
Which steps are endothermic? exothermic?
Time for an experiment… (Investigate This 2.2)
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
ethanol,colorless liquid in vial
urea,white crystals in vial
H2O
in pipet
Investigate This 2.2
Add water to urea until the vial is ~1/2 full. Recap the vial and swirl to dissolve. Does the solution become warm or cool?
Add water to ethanol until the vial is ~full, cap, and mix. What happens?
Does this describe ethanol dissolving? Urea dissolving?
The diagram shows changes in the solute only.
Predicting Solubility (Investigate This 2.5)
methanolCH3OH
hexaneCH3CH2CH2CH2CH2CH3
1-butanolCH3CH2CH2CH2OH
Which solute is most soluble in water?
Polar Solute + Water
methanolCH3OH Type of Solute-
Solvent IMFs?
Non-Polar Solute + Water
hexaneCH3CH2CH2CH2CH2CH3 Type of Solute-
Solvent IMFs?
1-butanolCH3CH2CH2CH2OH
Water + Solute with Polar/Non-Polar Regions
Type of Solute-Solvent IMFs?
Dissolving of Ionic Compounds
Interactions Between Ions
Magnitude of attraction Ecoulomb q1q2/d
small ions of big charge have largest attractive forces
~400-4000 kJ/mol (huge!) accounts for high melting/boiling points
dion of charge q1 ion of charge q2
So,why do ionic compounds dissolve at all?
How can strong ion-ion forces be overcome?
Ion-Dipole Interactions
Ions can interact with polar molecules (dipoles)
Magnitude of attraction Ecoulomb q1q2/d
Increases with ion charge, dipole moment ~40-600 kJ/mole
ion dipole with partial charges
d
- +
Ion-Dipole Interactions Most important example is ion-water
Na+ + 6H2O [Na(OH2)6]+
E = -397 kJ/mole
Ion-Dipole Interactions Overcome Ion-Ion Forces
Energy Changes for NaCl Dissolving in Water
Like Dissolves Like
Type of Solute
Polar Molecules
Nonpolar Molecules
Ionic compounds
Soluble in
polar solvents (water, methanol, acetone)
nonpolar or slightly polar solvents (C6H6, CCl4, CHCCl3)
very polar solvents (water)
Solute-Solvent IMF
dipole-dipole or H-bonding
dispersion or weak dipole-dipole attractions
ion-dipole attractions