•WE’RE IN THE HOME STRETCH!•FINAL EXAM ONE WEEK FROM TODAY @ 8AM

•MAKE UP LAB

•OWL ASSIGNMENT WILL BE POSTED WED., COMPLETE BY SATURDAYChapter 10: Gases (Mon. & Wed.)

Chapter 11: Intermolecular Forces and the Liquid State (Fri.)

December 7, 2009

Gases

Why gases?

What is a gas? State of matter where distance between particles is

much bigger than the particles

Properties of Gases

Property Common Unit Other UnitsSymbo

l

Mass grams (g) mg, kg -

Amount moles (mol) none n

Volume liters (L) mL V

Pressureatmosphere (atm)

bar, mmHg, psi, kPa

P

Temperature

Kelvin (K) ºC, ºF T

Properties of Gases: What is pressure?

Area

ForcePressure

Common Units of Gas Pressure

1 atm =

1.013 bar

101.3 kPa (kilopascal)

760 torr

760 mmHg (mm mercury)

14.7 psi (pounds per sq. inch)

Kinetic Molecular Theory (Sec. 10.6)

Molecules in a gas are always moving quickly and randomly

Average kinetic energy is determined by temperature

All gases at the same temperature have the same average kinetic energy, regardless of mass

Gas molecules collide with each other and the walls of their container without losing energy (“elastic” collisions)

Kinetic Energy of Gases

Kinetic energy of a single molecule

Average kinetic energy for a collection of molecules:

velocityvmassmwheremvKE ,2

1 2

molKatmL0.082057

KmolJ8.3145constantgas

,Kelvininetemperatur2

3

2

1 2

R

T

RTvmKE

How fast do molecules really move?

O2 gas at room temperature (25ºC = 298K)

Root-mean-square (rms) speed

molkginmassmolarMmolKJRM

RTvvrms /,/3415.8

32

Boltzmann Distribution

Gas molecules move with a range of speeds

Boltzmann Distribution

Boltzmann Distribution & Molar Mass

Boltzmann Distribution and Temperature

Boltzmann Distribution

Gas molecules move with a range of speeds

On average, gas molecules move faster at higher temperatures

Heavier gases move more slowly on average than lighter gases at the same temperature

Don’t confuse average kinetic energy with speed!

Which moves faster?

1 2 3

17%8%

75%1. O2 at 300 K

2. He at 300 K3. same

Which moves faster?

1 2 3

3%10%

87%1. O2 at 250 K

2. O2 at 300 K

3. same

Which has greater kinetic energy?

1 2 3

21%

65%

14%

1. O2 at 300 K

2. He at 300 K3. same

All the O2 molecules at 300 K move faster than all the molecules of O2 at 200 K.

1 2

66%

34%

1. true2. false