I. Physical Properties

Ch. 12 - GasesCh. 12 - Gases

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

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

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

D. TemperatureD. TemperatureD. TemperatureD. Temperature

ºF

ºC

K

-459 32 212

-273 0 100

0 273 373

32FC 95 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

exact height of the Hg depends on atmospheric pressure

usually measured in mm Hg

E. PressureE. PressureE. PressureE. Pressure

Manometer• measures contained gas pressure

U-tube Manometer

Difference in height in two arms of U-tube is measure of pressure of gas sample

measured in various different units

E. PressureE. PressureE. PressureE. Pressure

2m

NPa

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

G. Pressure Problem 1G. Pressure Problem 1G. Pressure Problem 1G. Pressure Problem 1

The average pressure in Denver, Colorado, is 0.830 atm. Express this in (a) mm Hg and (b) kPa.

(a) 0.830 atm

1 atm

760 mm Hg= 631

mm Hg

(b) 0.830 atm

1 atm

101.325 kPa= 84.1

kPa

G. Pressure Problem 2G. Pressure Problem 2G. Pressure Problem 2G. Pressure Problem 2

Convert a pressure of 1.75 atm to kPa and mm Hg.

(a) 1.75 atm

1 atm

101.325 kPa= 177

kPa

(b) 1.75 atm

1 atm

760 mm Hg= 1330

mm Hg

G. Pressure Problem 3G. Pressure Problem 3G. Pressure Problem 3G. Pressure Problem 3

Convert a pressure of 570. torr to atmospheres and kPa.

(a) 570 torr

760 torr

1 atm= .750

atm

(b) 570 torr

760 torr

101.325 kPa= 76.0

kPa