CHEM 123N Study Guide - Comprehensive Final Exam Guide - Solvent, London Dispersion Force, Intermolecular Force

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CHEM 123N
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Surface Tension
- Elastic behavior of liquid surface, makes it acquire least possible
surface area
- Surface molecules efel different forces than interior. Molecules or
atoms in the middle of a liquid are attracted equally in all directions,
but molecules or atoms on the surface feel attractive forces on only
one side and are thus drawn in toward the liquid.
- Generally, stronger IMFs = greater surface tension, but this is
temperature dependent.
Cohesion and Adhesion
Cohesive forces = IMFs that bind similar molecules to each other
Adhesive forces = IMFs that bind a substance to a surface.
Capillary action - Rise of liquids
up narrow tubes.
For example, water has stronger
adhesive forces with glass
[meniscus upward], whereas
mercury has stronger cohesive
forces [clings to itself].
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Supercritical Fluids
Gases liquefy if enough pressure is applied, the highest T at which a gas
can form a liquid if enough pressure is applied, called critical temperature
[T sub c]
- Aboe T sub c, as ca’t be liuiied o atte ho uch pessue is
applied.
Pressure required to liquefy a gas at its T sub c = critical pressure, P sub c.
T sub c increases with increasingly strong IMFs.
State beod T sub c ad P sub c, = supecitical luid, chaacteistics o
both liuids ad ases but it’s eithe - It can effuse through solids like a
gas, and dissolve materials like a liquid. [Table 11.6 for selected
substances]
Vaporization
- Some molecules at liquid surface have high enough KE to overcome
IMFs in liquid interior
- High-KE molecules escape liquid, become vapor (gas)
- Vapor exerts pressure
Vapor Pressure
- Surface molecules Ke distributed over a range
- Only small fraction have sufficient Ke to escape to become gas
[minimum KE needed to escape liquid phase]
- Liquid and vapor pressure reach dynamic equilibrium
- Boiling point - Temperature at which vapor pressure = atmospheric
pressure
- Normal boiling point -T at hich liuid’s apo pessue = 1at
- Natual lo o apo pessue is iesel popotioal to liuid’s
temperature [ln P alpha 1/T]
- Clausius - Clapeyron equation : ln P = [- delta H vap / R*T ] + C
- One point - ^
- Two point - ln p2/p1 = delta h vap / r ( (1/t2) -(1/t1) )
- P1 and p2 are vapor pressures of some liquid at two temps, T1
and T2, calculate P2 at T2 if you know P1 and T1 with delta h
vap.
Phase Diagram
Graph of P vs. T
- Temps where solid,liquid,gas are stable.
- Melting, boiling, sublimation T at different P
- Triple point and critical point labelled
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