UNIT 5: GASES & ATMOSPHERIC CHEMISTRY 11.1, 11.2 – The Basics of KMT and Pressure

STATES OF MATTER Two factors determine the state of a substance: The forces holding the particles together The kinetic energy of the particles (which tends to pull them apart)

GASES Gases uniformly fill a container There is a lot of space in between gas particles Most of the time, gas particles have no intermolecular forces present Remember your KMT…

MOLECULES/ATOMS OF GAS IN A CONTAINER Particles move in rapid movement and collide with each other or with walls of the container Compressible Each particle has its own kinetic energy, move independently The temperature of the gas = the average kinetic energy of the gas molecules

PRESSURE The force exerted by the moving gas particles on the sides of the container (per unit area) Atmospheric pressure is the force exerted on Earth’s surface by a column of air over a given area

MEASURING PRESSURE A barometer is a device for measuring air pressure Ex: mercury barometer A closed tube is filled with mercury, and then inverted into a pan. Gravity pulls the mercury downwards, but pressure pushes on the mercury in the pan, keeping it inside the tube The result is that we can measure the height of the Hg in the tube as a measure of pressure

This is where we get the units mmHg for pressure – millimeters of mercury

UNIT CONVERSION!! 1 atm = 760 mmHg 1 atm = kPa (kiloPascals) Also psi, bar… SAP (Standard Atmospheric Pressure) is: Atmospheric Pressure in dry air at sea level at 0°C 1 atm / 760 mmHg / kPa

PRACTICE! 0.76 atm = ?? kPa = ?? mmHg 0.76 atm x kPa = 77 kPa 1 atm 0.76 atm x 760 mmHg = mmHg 1 atm ?? atm = ?? kPa = 805 mmHg 1.06 atm = kPa

MORE PRACTICE! p. 435 # 1, 3