Pressure and Temperature William Thomson “Lord Kelvin”

Measuring Pressure The first device for measuring atmospheric pressure was developed by Evangelista Torricelli during the 17 th 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)  1 standard atmosphere (atm)  kPa (kilopascals)  14.7 lbs/in2  760 mm Hg (millimeters of mercury)  760 torr

Pressure UnitSymbolDefinition/Relationship PascalPaSI pressure unit 1 Pa = 1 newton/meter 2 Millimeter of mercury mm HgPressure that supports a 1 mm column of mercury in a barometer AtmosphereatmAverage atmospheric pressure at sea level and 0  C Torrtorr1 torr = 1 mm Hg Pressure is the force created by the collisions of molecules with the walls of a container

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 °C = Kelvins - 273

Standard Temperature and Pressure “STP” Either of these:  273 Kelvin (273 K)  0  C Either of these:  273 Kelvin (273 K)  0  C And any one of these: 1 atm  1 atm  kPa  14.7 lbs/in 2 (psi)  760 mm Hg  760 torr And any one of these: 1 atm  1 atm  kPa  14.7 lbs/in 2 (psi)  760 mm Hg  760 torr

Standard Molar Volume One mole of a gas at STP has a volume of 22.4 Liters

Mole Relationships Mole Atoms or molecules Atoms or molecules Liters Grams 6.02 x AtomicMassAtomicMass L 22.4 L