Vaporization, Viscosity, and
IMFs
Molecules in Consider This 1.40
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Do all liquids evaporate at the
same rate? (Consider This 1.40)



Equal volumes of H2O, methanol,
hexane on sponges
Wipe sponges on blackboard
Which liquid evaporates fastest?
slowest?
Relative energies of
vaporization? (Consider This
1.41)



Is DEvaporization + (endothermic) or (exothermic)?
Which liquid has the largest magnitude
DEvap?
Sketch an energy diagram to compare
the DEvap values of the three liquids.
Energy Level Diagram
(Investigate This 1.40)
H2O (g)
Methanol (g)
Energy
Hexane (g)
H2O, Methanol,
Hexane, (l) initially
DEvap(H2O) > DEvap(methanol) > DEvap(hexane)
How is DEvap related to IMFs?
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largest
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smallest DEvap
Two liquids about to be heated
(Consider This 1.53)
computer
interfaced
temperature
probes
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water
ethanol

Beakers contain equal
masses of water and
ethanol at room temp.

Why are the two
liquids not the same
volume?
Results of heating (1.53)

How are the
plots
different? The
same?

Equal energy
was added to
both liquids.
What
accounts for
the
differences
you see?
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Results of heating (1.53)

Heat absorbed


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disrupts IMFs
and then raises the
temperature
Water has stronger IMFs
(more extensive Hbonding), so more of the
heat is required to disrupt
the IMFs. Less heat is
available to raise the
temperature.

water has a higher
specific heat
Viscosity



Resistance to flow
Increases as IMFs get stronger
Decreases as temperature increases
IMFs in Glycerol?
H2COH
H bond between two glycerol molecules
HCOH
H2COH ….. OCH2
H
HCOH
HOCH2
Viscosity of Glycerol as f(T)
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