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Lecture 6

CHEM 202 Lecture Notes - Lecture 6: Pentane, Miscibility, Soft Drink

Course Code
CHEM 202
Neal Stolowich

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Class 6
Reminder- 7pm recitation sections now in CB-329
Sapling Quiz 1 will be available this week (Thursday?)
Chap 40 Review- Role of entropy in solubility in water (sec 40.1)
Take to the bank- For Gases, entropy always opposes dissolution.
For Molecular Solids, entropy usually favors dissolution
For liquids and ionic solids, can go either way.
Solubility ultimately is derived from both enthalpy and entropy considerations. (sec 40.2)
Gases- most gases are insoluble due to entropy. Only when enthalpy becomes favorable, then you
have appreciable solubility. (ie, NH3 – why?)
Liquids- more complicated, but usually enthalpy driven (Hovap vs. Hohydr)
Molecular solids- Hosoln vs. Sosoln , both usually positive
Ionic solids- Hosoln vs. Sosoln; both usually can go either way.
2) Hydrophobic, Hydrophilic, Amphiphilic (sec 40.3)
Hydrophobic – aversion to water (the solute is the hydrophobe). Can pertain to whole molecule or
parts of a molecule. Pentane is a hydrophobe; the butyl part of butanol is hydrophobic.
Hydrophilic – tendency for water, ie – ‘water loving’ (the solute is the hydrophile)
Ammonia is a hydrophile; the OH part of butanol is hydrophilic.
Amphiphilic – molecules that possess both characteristics, ie – butanol.
3) Balance in perspective (sec 40.4)
Beginning in Chap34, the properties of pure substances and simple phases were discussed with
relationship to enthalpy and entropy. Chap 39 (enthalpy) and Chap 40 (entropy) further applied these
principles for the analysis of mixtures: enthalpy on the basis of breaking and forming intermolecular
forces, and entropy in terms of increasing order or disorder. The balance between these two will come to
a grander scale in ensuing chapters….
Solution Equilibria (chap 41)
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