Properties of Gases Gases expand to fill any container. –random motion, no attraction Gases are fluids (like liquids). –particles flow easily Gases have very low densities. –lots of empty space; particles spaced far apart Gases are easily compressible. –empty space reduced to smaller volume Courtesy Christy Johannesson

Kinetic Molecular Theory Postulates of the Kinetic Molecular Theory of Gases 1.Gases consist of tiny particles (atoms or molecules) 2.These particles are so small, compared with the distances between them, that the volume (size) of the individual particles can be assumed to be negligible (zero). Gases have low densities. 3. The particles are in constant random straight-line motion, colliding with the walls of the container. These collisions with the walls cause the pressure exerted by the gas. 4. The particles are assumed not to attract or to repel each other. 5. The average kinetic energy of the gas particles is directly proportional to the Kelvin temperature of the gas

Collisions of Gas Particles Pressure = collisions on container walls

In a smaller container - particles have less room to move. Particles hit the sides of the container more often. This causes an increase in pressure. As volume decreases: pressure increases. Changing the Size of the Container

Pressure = Force/Area KEY UNITS AT SEA LEVEL (also known as standard pressure) kPa (kilopascal) 1 atm 760 mm Hg 760 torr 14.7 psi Courtesy Christy Johannesson Sea level

Pressure and Balloons A B = pressure exerted ON balloon A = pressure exerted BY balloon B When balloon is being filled: P A > P B When balloon is filled and tied: P A = P B When balloon deflates: P A < P B

When the balloons are untied, will the large balloon (A) inflate the small balloon (B); will they end up the same size or will the small balloon inflate the large balloon? Why? Balloon Riddle A B C

Barometers Mount Everest Sea level On top of Mount Everest Sea level

Temperature ºF ºC K K = ºC Always use temperature in Kelvin when working with gases. Std temperature = 273 K Courtesy Christy Johannesson

STP Standard Temperature & Pressure 0°C 273 K 1 atm kPa - OR - STP Courtesy Christy Johannesson

Boyle’s Law 1 atm 4 Liters As the pressure on a gas increases 2 atm 2 Liters As the pressure on a gas increases - the volume decreases Pressure and volume are inversely related

Boyle’s Law Illustrated Zumdahl, Zumdahl, DeCoste, World of Chemistry  2002, page 404

b The pressure and volume of a gas are inversely related at constant mass & temp Boyle’s Law PV = k Courtesy Christy Johannesson Volume (mL) Pressure (torr) P. V (mL. torr) x x x x 10 3 P 1 x V 1 = P 2 x V 2

Boyle’s Law example A quantity of gas under a pressure of kPa has a volume of 380 cm 3. What is the volume of the gas at standard pressure, if the temperature is held constant? P 1 x V 1 = P 2 x V 2 (106.6 kPa) x (380 cm 3 ) = (101.3 kPa) x (V 2 ) V 2 = 400 cm 3

Charles’s Law Timberlake, Chemistry 7 th Edition, page 259

If you start with 1 liter of gas at 1 atm pressure and 300 K and heat it to 600 K one of 2 things happens 300 K

Either the volume will increase to 2 liters at 1 atm 300 K 600 K

300 K 600 K Or the pressure will increase to 2 atm.

The volume and absolute temperature (K) of a gas are directly related –at constant mass & pressure Charles’ Law Courtesy Christy Johannesson Volume (mL) Temperature (K) V / T (mL / K) V 1 / T 1 = V 2 / T 2