viscosity a liquids resistance to flow high viscosity high resistance to flow depends on IMFs as temp increases viscosity decreases Molecules on a liquids surface ID: 314837
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Slide1
Some Properties of Liquids
viscosity: a liquid’s resistance to flow
-- high viscosity =
high resistance to flow
-- depends on IMFs
--
as temp. increases, viscosity decreases Slide2
Molecules on a
liquid’s surface experience anet inward force
--
this reduces surface area and “packs together”
m’cules on surface
surface tension
: the energy required to increase a
liquid’s surface area by 1 m
2
--
--
water has a high surface tension due to HBFs
a measure of the “tightness” of a surface’s “skin” Slide3
cohesive forces: IMFs that bind...
adhesive forces: IMFs that bind...
similar m’cules
to each other
a substanceto a surface
--
their relative magnitude determines theshape of a meniscus
adhesion cohesion
adhesion cohesion
>
<
meniscus: H
2
O
meniscus: HgSlide4
capillary action: the rise of liquids up narrow tubes
-- adhesion _________ the liquid,
while cohesion…
“stretches”
keeps it together
In green plants, capillary action draws waterthrough narrow tubes, collectively called xylem.Slide5
Why does liquid go up narrow tubes
farther than up thick tubes?
adhesion force
2
p
r
p
r
2
=
Liquid stops rising
under this condition.
gravity
gravity
If tube
diameter increases
by a factor of 10:
adhesion increases 10X;
liquid’s weight increases 100X. Slide6
Will a “plug” of liquid continue inching its way up a tube?
As soon as plug breaks free from rest
of liquid, “down” adhesion forces appear,
which equal “up” adhesion forces.
But there’s also gravity, so “down” wins.
Assume
there is a plug that
wants to break free…
“No creeping plugs.”
Adhesion forces pull it up.
Plug drops until “up” adhesion
equals gravity.