formation of gases
:
many elements and compounds are already gases at room temperature
sublime – when solids are heated and turned into gases
vaporize – when liquids are heated and turned into gases
gases are characterized by pressure, volume, and temperature
gas:
composed of particles (atoms or molecules) in constant and random motion
pressure
:
pressure is related to force
force = mass * acceleration (F=ma)
acceleration = change in velocity (m/s
2
)
mass (in kilograms) times acceleration (in meters per second squared) = force (in kilograms times
meters per second squared which equals Newton’s)
pressure =
force
(P = F/A)
area
pressure is measured in Newton’s
which is equivalent to 1 Pascal
m
2
volume
:
a solid has its own shape and volume
a gas forms to the container and fills the entire container
a liquid occupies a portion of a container
the volume of a gas equals the volume of the container
volume of containers:
box: volume = length*width*height (V=lwh)
sphere: volume = 4/3*
π
*radius
3
(V=4/3
π
r
3
)
cylinder: volume =
π
*radius
2
*height (V=
π
r
2
h)
atomic pressure
:
measured by a barometer
the pressure of the atmosphere is equal to the pressure of the supported column of mercury in a barometer
pressure doesn’t depend on the radius of the cylinder
the pressure of mercury equals density*height*gravity (P=dhg) which also equals the atmospheric pressure
barometer equations:
atmospheric pressure = density of the liquid*height of the liquid*gravity (P
atm
=d
l
h
l
g
l
)
if your comparing liquids:
density of mercury*height of mercury = density of liquid*height of liquid
(d
Hg
h
Hg
=d
l
h
l
)
the standard atmospheric pressure supports a column of mercury 760mm high
the unit “mm Hg” is called a torr
atmospheric pressure is related to weather
high pressure= cloudless, sunny day
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low pressure= clouds, storms, rain
really low pressure= tornadoes and hurricanes
when you suck on a straw to drink a coke you create a partial vacuum
example problem:
If the barometer pressure is 763 torr, what height would the water be?
The density of Hg is
13.6 g/mL and the density of water is 1 g/mL
need to know:
atmospheric pressure supports a column of mercury 763 mm high
P
atm
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 Spring '06
 staff
 gas particles

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