CHAPTER 5 - GASES
DR. ED TAVSS
Partial pressure (mixtures of gases)
Kinetic molecular theory/Effusion and Diffusion/Real gases
CHEM 161-2006 EXAM II
In the above drawing, the value of h, the height of the liquid in the tube above the liquid in the beaker, would
depend on which of the following?
Cross sectional area of the tube
Y and Z only
X and Y only
X and Z only
X, Y, and Z
This is a barometer.
The liquid is held in the tube by atmospheric pressure.
If the atmospheric pressure is exactly 1
atmosphere (14.7 lb/in
), then the liquid would have to exert a pressure of 14.7 lb/in
(X) If the liquid was, let’s say, less dense, then it would have to be a greater height to exert a pressure of 14.7 lb/in
If the liquid was more dense then it would have to be a shorter height.
(Y) The cross sectional area of the tube is irrelevant, since the pressure (14.7 lb/in
) would be the same regardless of
the cross-sectional area.
(Z) If the atmospheric pressure decreased, then the height would decrease because it would require less liquid to be
equal to a lower pressure.
If the atmospheric pressure increased, then the height would need to increase.
Chem 161-2005 Hourly Exam II
Chapter 5 - Gases
Which of the following is a unit of pressure?
Pressure is force per unit area.
A is force per unit volume.
B is force per unit volume
C is force
D is force per unit area.
E is force per unit area.
The acceptable answer is “D”.
“E” should also be
Some faculty members consider “N” as force, and “g” as mass.
Since pressure is
force per unit area then only “D” is allowed.
In my opinion this is nit-picking semantics.
Chem 162-2004 Hourly exam II
Chapter 5 - Gases
Mercury, rather than water, is used as a liquid in barometers because:
Mercury is more sensitive to pressure changes than water.
Mercury is safer.
Pressure is measured in mm of mercury.
Mercury is denser.
Mercury is metallic.
A barometer works by the pressure of the air (e.g., 1 atmosphere) being equal and
opposite to the pressure exerted by the liquid in the barometer.
The pressure exerted by
the liquid in the barometer is due to its height and its mass.
For mercury, this height is
Since water has a density 13.6 times less than the density of mercury, it would
require a height of 760 mm x 13.6 = 10336 mm = 33.9 feet, and therefore would be too
cumbersome to be useful.
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