The weight of Earth’s atmosphere above us exerts a pressure on us. In a way, we live at the bottom of an ocean of air.

Atmospheric Pressure Atmospheric pressure changes with altitude and with weather conditions. Standard pressure is the average pressure of our atmosphere at sea level. 1.0 atmosphere 760 mm Hg (mercury) 14.7 lb/in 2 (psi) kilopascals

Mercury Hg 760 mm Hg Atmospheric Pressure No pressure (vacuum) = Standard Pressure A Mercury Barometer 1.0 atmosphere

Atmospheric Pressure 725 mm Hg decreases Pressure is measured by how far it pushes mercury up a tube. If the weather changes, or if the pressure is measured at higher elevations…

American System Pressure is measured in psi (lb/in 2 ) 1 inch 14.7 pounds The weight of the atmosphere is 14.7 pounds on every square inch area. That’s about 4 or 5 of your Chemistry books.

International System (SI) 1 meter The international way of measuring pressure uses Newtons per square meter. mass x gravity = Newton (force) Newtons/m 2 = Pascal 101,325 Newtons/m 2 = 101,325 Pascals kiloPascals > 10 tons kPa

760 mm Hg = 760 torr Standard Pressure Pressure can be measured in different units. Meteorologists use another way for measuring pressure (like in hurricanes). 1.0 atmosphere (atm) 14.7 lb/in 2 (psi) kiloPascals (kPa) 1013 millibars is standard pressure.

If the recommended tire pressure is 32 psi, (a)What is the equivalent pressure in atmospheres? (b) in kPa? 32 psi x ________ psi atm = 2.18 atm psi x __________ psi kPa = 220 kPa More than twice atmospheric pressure. 1.0 atmosphere 760 mm Hg 14.7 lb/in 2 (psi) kilopascals

750 mm Hg Manometer

200 mm 750 mm Hg mm 950 mm Hg Manometer

100 mm 750 mm Hg mm 650 mm Hg Manometer

150 mm 765 mm Hg mm 915 mm Hg Manometer ? mm Hg

Celsius Kelvin 100 o C 0oC0oC 0 Kelvin water boils water freezes absolute zero -273 o C 273 o 25 o C? K298 K ? K 273 K = ? K373 K o C = Kelvin To change Celsius to Kelvin, add 273