KINETIC MOLECULAR THEORY OF GASES Balloon Dog Orange

KINETIC MOLECULAR THEORY OF GASES “Balloon Dog, Orange Sculpture” Jeff Koons (sold for $52, 000 dollars in 2013!)

KINETIC MOLECULAR THEORY OF GASES 1. A gas consists of very small particles, each of which has a mass. Example: An inflated basketball weighs more than a deflated basketball.

KINETIC MOLECULAR THEORY OF GASES 2. The distances separating gas particles are large relative to the size of the particles. The volume of the gas particles is assumed to be zero because it is negligible compared with the total volume in which the gas is contained.

KINETIC MOLECULAR THEORY OF GASES Gas

KINETIC MOLECULAR THEORY OF GASES Liquid

KINETIC MOLECULAR THEORY OF GASES Solid

KINETIC MOLECULAR THEORY OF GASES 3. Gas particles are in constant, rapid, random motion. Gases immediately fill a container and quickly diffuse from one area to another. This is a good description of how gas molecules behave.

KINETIC MOLECULAR THEORY OF GASES http: //comp. uark. edu/~jgeabana/mol_dyn/Kin. Th. I. html http: //mutuslab. cs. uwindsor. ca/schurko/animations/ideal gas/ideal. Gas. htm

KINETIC MOLECULAR THEORY OF GASES 4. Collisions of gas particles with each other or with the walls of the container are perfectly elastic (no kinetic energy is lost). Unlike “bouncing balls, ” no energy of motion is lost.

KINETIC MOLECULAR THEORY OF GASES 5. The average kinetic energy of gas particles depends only on the temperature of the gas. The kinetic energy of gas molecules is proportional to their temperature in Kelvin. KE = ½ mv 2 High T Higher KE Low T Lower KE

KINETIC MOLECULAR THEORY OF GASES 6. Gas particles exert no force on one another. Attractive forces between gas particles is assumed to be zero. Depending on the gas, this can be good or bad assumption. For instance, H 2 O vapor has much stronger intermolecular interactions than He.

IDEAL GASES • Gases that follow the KMT are called Ideal Gases. In reality, there are no ideal gases, only real gases. • Real gases slightly attract each other and the particles do have volume. • However, at low pressures and large volumes, gases behave more ideally. • Helium behaves the most ideally. Why?

TEMPERATURE A measure of the average kinetic energy of the particles in a sample of matter.

TEMPERATURE T (˚C) Kinetic Energy (J)

TEMPERATURE What are the units? • Fahrenheit (˚F) • Celsius (˚C) • Kelvin (K)

TEMPERATURE So what’s the difference between the units of temperature? Where they place zero and the scale!

TEMPERATURE Celsius: Based on freezing and boiling points of water. 0˚ C = Freezing point of water 100 ˚C = Boiling point of water (at sea level)

TEMPERATURE Fahrenheit: Based on freezing point of sea water and average temperature of human. 0 ˚F = Freezing point of sea water 100 ˚F = Avg. temp. of human (measurement was off!)

TEMPERATURE Kelvin: Same unit as Celsius, but zero is placed at absolute zero 0 K = absolute zero = temperature at which all molecular motion stops

TEMPERATURE Conversions: TF = 1. 8(TC) + 32

Practice: TF = 1. 8(TC) + 32 25˚C = ? ˚F Ans: 77 ˚F

Practice: TF = 1. 8(TC) + 32 100. ˚F = ? ˚C Ans: 37. 8 ˚C

Temperature Conversions: TK = TC + 273

TK = TC + 273 Practice: 25˚C = ? K Ans: 298 K

TK = TC + 273 Practice: 328 K = ? ˚C Ans: 55 ˚C

Pressure The force per unit of area on a surface. • A gas uniformly fills any container, is easily compressed, and mixes completely with any other gas. • One of the most obvious and useful properties of a gas is that it exerts pressure on its surroundings. This is due to the particles hitting surfaces. • Atmospheric pressure, for example, is the result of a mass of air (a mixture of many gases in the atmosphere) being pulled down toward the center of the earth by gravity.

Pressure Mathematically, it looks like this:

Pressure So is P directly related to F or A? P P F A

Pressure So what are some units of pressure? • atm (atmosphere) • psi (pounds per square inch) • torr • mm. Hg (millimeters of mercury) • Pa (Pascal) • k. Pa (kilo Pascal) • bar

Pressure And here are the conversion factors: 1 atm = 14. 7 psi = 760 torr = 760 mm. Hg = 29. 92 in Hg = 101, 325 Pa = 101. 325 k. Pa = 1. 01325 bar

Pressure Let’s do some practice conversions: 689 torr = ? atm Ans = 0. 907 atm

Pressure Let’s do some practice conversions: 156. 1 k. Pa = ? psi Ans = 22. 7 psi

• A common condition for gas law problems is called “STP” or “Standard Temperature and Pressure. ” When a problem says a gas is at STP, o. C T=0 (exactly) and P = 1 atm (exactly

GOOD JOB!!! Now for your homework…