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**Pressure and Temperature**

William Thomson “Lord Kelvin”

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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.

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**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

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An Early Barometer The normal pressure due to the atmosphere at sea level can support a column of mercury that is 760 mm high.

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Pressure is caused by the collisions of molecules with the walls of a container is equal to force/unit area can be measured using a variety of units

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**Pressure Pressure is the force created by the collisions**

of molecules with the walls of a container Unit Symbol Definition/Relationship Millimeter of mercury mm Hg Pressure that supports a 1 mm column of mercury in a barometer Torr torr 1 torr = 1 mm Hg Pascal Pa SI pressure unit 1 Pa = 1 newton/meter2 Atmosphere atm Average atmospheric pressure at sea level and 0 C

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**Standard Pressure 760 torr 760 mm Hg (millimeters of mercury)**

101.3 kPa (kilopascals) 1 standard atmosphere (atm)

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**Converting Pressure Units**

Gas law problems involving pressure require that the pressure be in the SAME UNITS! 1 atm = kPa = 760 mm Hg Converting kPas to atms x atms = ____ kPas 1atm kPa Converting kPas to mm Hg x mm Hg = ____ kPas 760 mm Hg kPa

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**Converting Pressure Units**

1 atm = kPa = 760 mm Hg A gas sample has a pressure of mmHg. What is the pressure of this gas sample in atmospheres and in kilopascals? Converting mm Hg to atms x atms = 800 mm Hg 1atm mm Hg Converting mm Hg to kPas x kPas = 800 mm Hg 101.3 kPa 760 mm Hg x = atm x = kPa

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**Converting Pressure Units**

1 atm = kPa = 760 mm Hg A tank of oxygen is under a pressure of about 4.00 x 103 kPa. Express this pressure in millimeters of mercury. Converting kPas to mm Hg x mm Hg = 4 x 103 kPas 760 mm Hg kPa x = 3.00 x 104 mm Hg

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**Air Pressure has many applications (in real life!)**

Here’s one of those applications !

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The Kelvin Scale

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**Standard Temperature Standard Temperature equals: 273 Kelvin (273 K)**

0 C

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**Converting Celsius to Kelvin**

Gas law problems involving temperature require that the temperature be in KELVINS! Kelvins = C + 273 °C = Kelvins - 273

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**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 760 mm Hg 760 torr

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