Tests…..50% …….30% ??? Let’s vote

Kinetic Theory of Gases CH 13 and CH 14

Postulate #1 Particles in a gas are small, hard spheres with insignificant volume Particles are very far apart Lots of empty space between the particles No attraction/repulsion between the particles

Postulate #2 Particles in a gas are in constant, random motion Motion is fast “Fill” containers regardless of shape Uncontained gas can spread out into space without limit Particles travel in straight lines until they collide with something Estimates put speed of Oxygen molecules at 20 degrees Celsius at 117km/hr (~72 mi/hr) Odor from pizza would reach Mexico City from Washington DC in 115 minutes! Does that really happen? NO! molecules run into stuff and bounce around…rarely go in a straight line for long

Postulate #3 All collisions between particles in a gas are perfectly elastic KE is transferred without loss from one particle to another Total KE remains constant (really???)

Rules for discussing gases Temperature (T) Pressure (P) Volume (V) # particles (n) Must use Kelvin atm (atmospheres) kPa (kilopascals) mmHg (mm mercury L (liters) mL (milliLiters) in3 (inches cubed) cm3 Need to know if the number of molecules in a container is constant or not K = C + 273 1 atm = 101.3 kpa = 760 mmHg 1 cm3 = 1 mL Cannot use Celsius or Fahrenheit Sometimes see psi (pounds per square inch)

Why Worry about these variables? Pressure is a measure of how many times gas particles are hitting the sides of the container More hits = more pressure Increasing temperature = increase in KE Molecules are moving faster and hit the sides more often Results in an increase in pressure Changing the volume will affect pressure Smaller container with same number of molecules = more pressure Larger container with same n = less pressure Changing the number of molecules will affect pressure as well Which of these are variables are changing and which are constant must always be specified.

Homework P417 #1-6 Due tomorrow