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