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Lecture 1

CHEM 202 Lecture Notes - Lecture 1: Vaporization, Chemical Bond, Intermolecular Force

Course Code
CHEM 202
Neal Stolowich

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Phases, Part 1 (Chapter 34)
Solids: classified by particles in close proximity, usually in a fixed, locked arrangement. The
particles can vibrate or rate, but cannot move out of their fixed location. Solids have a definite
shape and volume.
Liquid: particles while also in close proximity, are in loose contact and are in motion. They
constantly bump or slide against each other, and can occupy any location within a liquid. It
occupies a definite volume, but sine there is no fixed arrangement, their shape conforms to the
Gas: particles are widely separated, seldom in contact with each other. They move freely at a
range of speeds and can be anywhere. NO definite volume or shape.
Entropy is a term used to describe the amount of disorder in a system and can be mathematically be
defined (it’s a thermodynamic function). It is a good thing. In the case of phases, entropy favors the gas
Entropy=options, the more the better!
Fewer restrictionsmore optionshigher entropy
More restrictionless options low entropy
Chemical bonding (intra-) and intermolecular forces (IF) bind and attract atoms, ions, and molecules.
This is the “glue” that favors the solid and liquid phases.
The why a compound exist in a particular phase is because of which of the above two phenomenon
dominates under a particle condition, or the balance between the two.
The gas phase has a lot of entropy but very weak if any Ifs; it is the favored phase by entropy alone. If
the Ifs are strong enough, the liquid phase can be obtained, and this phase has lower entropy (less
options). Finally the solid phase, the IF dominates, and a ordered, low entropy system is obtained.
Intermolecular forces
Note the different in gap. The jump from liquid to gas is bigger.
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Phase changes
Fusion (melting):
Freezing: liquid to solid
Vaporization: liquid to gas
Solidliquid and liquidgas=solidgas
Ex. Let’s look at the enthalpy in the process of heating 15.0 g of H2O from 40 degree C to 100 degree C
(pg 356)
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