Pressure Pressure and and
TemperatuTemperaturere
William Thomson“Lord Kelvin”
CA StandardsCA Standards
Measuring Measuring PressurePressure
The first device for measuring atmosphericpressure was developed by Evangelista Torricelli during the 17th century.
The device was called a “barometer”
Baro = weight Meter = measure
An Early An Early BarometerBarometer
The normal pressure due to the atmosphere at sea level can support a column of mercury that is 760 mm high.
PressurePressureIs caused by the collisions of Is caused by the collisions of
molecules with the walls of a molecules with the walls of a containercontainer
is equal to force/unit areais equal to force/unit area
Standard Standard PressurePressure
1 standard atmosphere (atm)1 standard atmosphere (atm) 101.3 kPa (kilopascals)101.3 kPa (kilopascals) 14.7 lbs/in214.7 lbs/in2 760 mm Hg (millimeters of mercury)760 mm Hg (millimeters of mercury) 760 torr760 torr
PressurePressure
Unit Symbol
Definition/Relationship
Pascal Pa SI pressure unit1 Pa = 1 newton/meter2
Millimeter of mercury
mm Hg Pressure that supports a 1 mm column of mercury in a barometer
Atmosphere atm Average atmospheric pressure at sea level and 0 C
Torr torr 1 torr = 1 mm Hg
PressurePressure is the force created by the is the force created by the collisionscollisions
of molecules with the walls of a containerof molecules with the walls of a container
(KE) 32avg RT
Kelvin temperature is an index of the random motions of gas particles (higher T means greater motion.)
Kinetic Energy of Gas Kinetic Energy of Gas ParticlesParticlesAt the same conditions of temperature, all
gases have the same average kinetic energy.
2
21 mvKE
The Kelvin ScaleThe Kelvin Scale
Standard TemperatureStandard Temperature
Standard Temperature Standard Temperature equals:equals: 273 Kelvin (273 K)273 Kelvin (273 K) 0 0 CC
Converting Celsius to KelvinConverting Celsius to KelvinGas law problems involving temperature require that the temperature be in KELVINS!
Kelvins = Kelvins = C + 273C + 273
°C = Kelvins - 273°C = Kelvins - 273
Standard Standard Temperature Temperature andand Pressure Pressure
“STP”“STP”
Either of these: 273 Kelvin (273 273 Kelvin (273 K)K) 0 0 CC
And any one of these: 1 atm1 atm 101.3 kPa101.3 kPa 14.7 lbs/in14.7 lbs/in2 2 (psi)(psi) 760 mm Hg760 mm Hg 760 torr760 torr
TEMPERATURE
PRESSURE
K oC mm Hg kPa atm
373 K 890 mm Hg
56oC 123 kPa
154oC 0.64 atm
128 K 3140 mm Hg
800 K 2.35 atm
–10oC 25 kPa