Pressure and Temperature William Thomson “Lord Kelvin”

CA Standards Students know the values and meanings of standard temperature and pressure (STP). Students know how to convert between the Celsius and Kelvin temperature scales. Students know there is no temperature lower than 0 Kelvin.

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 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

Kinetic Energy of Gas Particles The Meaning of Temperature Kelvin temperature is an index of the random motions of gas particles (higher T means greater motion.) Kinetic Energy of Gas Particles At the same conditions of temperature, all gases have the same average kinetic energy.

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

Standard Temperature and Pressure “STP” Either of these: 273 Kelvin (273 K) 0 C Standard Temperature and Pressure “STP” And any one of these: 1 atm 101.3 kPa 14.7 lbs/in2 (psi) 760 mm Hg 760 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