Physical PropertiesPhysical

Properties

Ch. 10 & 11 - Ch. 10 & 11 - GasesGases

A. Kinetic Molecular A. Kinetic Molecular TheoryTheoryA. Kinetic Molecular A. Kinetic Molecular TheoryTheory

Particles in an ideal gas…• have no volume.• have elastic collisions. • are in constant, random, straight-

line motion.• don’t attract or repel each other.• have an avg. KE directly related to

Kelvin temperature.

Ideal Gases donIdeal Gases don’’t existt existIdeal Gases donIdeal Gases don’’t existt exist

Molecules do take up space

• All matter has volumeThere are attractive forces

• otherwise there would be no liquids

Ideal GasesIdeal GasesIdeal GasesIdeal Gases

There are no gases for which this is true.

Real gases behave this way at high temperature and low pressure.

Ideal GasesIdeal GasesIdeal GasesIdeal Gases

In this chapter we are going to assume the gases behave ideally

Does not really exist • makes the math easier • close approximation.

Assume particles have no volumeAssume no attractive forces

between molecules

B. Real GasesB. Real GasesB. Real GasesB. Real Gases

Particles in a REAL gas…

• have their own volume

• attract each other

Gas behavior is most ideal…

• at low pressures

• at high temperatures

• in nonpolar atoms/molecules

Real Gases behave like Real Gases behave like Ideal GasesIdeal GasesReal Gases behave like Real Gases behave like Ideal GasesIdeal Gases

When the molecules are far apart

They take a smaller percentage of the space

Ignoring their volume is reasonable

This is at low pressure

Real Gases behave like Real Gases behave like Ideal gases whenIdeal gases whenReal Gases behave like Real Gases behave like Ideal gases whenIdeal gases when

Molecules are moving fast.Molecules are not next to each

other very longAttractive forces can’t play a role.At high temp.Far above boiling point.

C. Johannesson

C. Characteristics of C. Characteristics of GasesGasesC. Characteristics of C. Characteristics of GasesGasesGases expand to fill any container.

• random motion, no attraction

Gases are fluids (like liquids).• no attraction

Gases have very low densities.• no volume = lots of empty space

C. Characteristics of C. Characteristics of GasesGasesC. Characteristics of C. Characteristics of GasesGasesGases can be compressed.

• no volume = lots of empty space

Gases undergo diffusion & effusion.• random motion

DiffusionDiffusionDiffusionDiffusion

Molecules moving from areas of high concentration to low concentration.

Perfume molecules spreading across the room.

Effusion - Gas escaping through a tiny hole in a container.

From high to low concentration Both depend on the speed of the

molecules

C. Johannesson

D. TemperatureD. TemperatureD. TemperatureD. Temperature

ºF

ºC

K

-459 32 212

-273 0 100

0 273 373

K = ºC + 273

Always use absolute temperature (Kelvin) when working with gases.

E. PressureE. PressureE. PressureE. Pressure

area

forcepressure

Which shoes create the most pressure?

E. PressureE. PressureE. PressureE. Pressure

Barometer• measures atmospheric pressure

Mercury Barometer

Aneroid Barometer

E. PressureE. PressureE. PressureE. Pressure

Manometer• measures contained gas pressure

U-tube Manometer Bourdon-tube gauge

E. PressureE. PressureE. PressureE. Pressure

2m

NkPa

KEY UNITS AT SEA LEVEL

101.325 kPa (kilopascal)

1 atm

760 mm Hg

760 torr

14.7 psi

F. STPF. STPF. STPF. STP

Standard Temperature & PressureStandard Temperature & Pressure

0°C 273 K

1 atm 101.325 kPa-OR-

STP