Transcript A Gas

Pressure
and
Temperature
William Thomson
“Lord Kelvin”
NM Standards
Students know9-12 Benchmark III: Understand the
motion of objects and waves, and the forces that cause them.
Students know how to convert between
the Celsius and Kelvin temperature
scales.
Students know the relationship between force and
pressure, and how the pressure of a volume of gas depends on the
temperature and the amount of gas.
Measuring Pressure
The first device for
measuring atmospheric
pressure was developed by
Evangelista Torricelli
during the 17th century.
The device was called a
“barometer”
Baro = weight
Meter = measure
An Early
Barometer
The normal pressure due
to the atmosphere at
sea level can support a
column of mercury that
is 760 mm high.
Pressure
Is caused by the collisions of
molecules with the walls of a
container
is equal to force/unit area
Standard Pressure
 1 standard atmosphere (atm)
 101.3 kPa (kilopascals)
 14.7 lbs/in2
 760 mm Hg (millimeters of mercury)
 760 torr
Pressure
Pressure is the force created by the collisions
of molecules with the walls of a container
Unit
Symbol
Definition/Relationship
Pascal
Pa
SI pressure unit
1 Pa = 1 newton/meter2
Millimeter of
mercury
mm Hg
Atmosphere
atm
Torr
torr
Pressure that supports a 1 mm
column of mercury in a
barometer
Average atmospheric pressure
at sea level and 0 C
1 torr = 1 mm Hg
Manometer
An open manometer is filled with mercury and
connected to a container of hydrogen gas. The
mercury level is 57 mm higher in the arm of the
tube connected to the hydrogen. If the
atmospheric pressure is 0.985 atm, what is the
pressure of the hydrogen gas, in atmospheres?
• An open manometer connected to a
tank of argon has a mercury level 83
mm higher in the atmospheric arm. If
the atmospheric pressure is 76.9 kPa,
what is the pressure of the argon in
kPa?
Another problem
• An open manometer is filled with
mercury. The mercury level is 12 mm
higher on the side open to the
atmosphere. What is the total
pressure of the gas, in kPa, if the
atmospheric pressure is 100.8 kPa?
The Kelvin Scale
Standard Temperature
Standard Temperature equals:
 273 Kelvin (273 K)
 0 C
Converting Celsius to Kelvin
Gas law problems involving temperature
require that the temperature be in
KELVINS!
Kelvins = C + 273
°C = Kelvins - 273
Either of these:
 273 Kelvin (273 K)
 0 C
And any one of these:
 1 atm
 101.3 kPa
 14.7 lbs/in2 (psi)
 760 mm Hg
 760 torr
Standard
Temperature and
Pressure
“STP”