Gases

Properties and Behavior of Gases

General Properties of Gases
Properties

Solids

Shape

Definite shape

Volume

Definite volume

Particles and movement Compressibility
Density

Liquids

Gases

No definite shape No definite shape
Definite volume No definite volume

Particles are
Particles are close close together together and and may vibrate move randomly in place
Incompressible

Slightly compressible Particles are far apart and move randomly Very compressible

ρsolid > ρliquid >>>ρgas

Substances that Exist as Gases
(@ normal conditions = 25 °C, 1 atm)
Elements

Compounds

H2
N2
O2
F2
Cl2
He
Ne
Ar
Kr
Xe
Rn

HF
HCl
HBr
HI
CO
CO2
NH3
NO
NO2
N2O
SO2
H2S
HCN

Pressure pressure pressure



force force area area SI:

1 N m-2 = 1 kg m-1 s-2 = pascal (Pa)

Unit conversions:
1 atm = 101,325 Pa = 101.325 kPa
1 bar = 105 Pa = 100 kPa
1 atm = 1.01325 bar
1 bar = 0.9869 atm
1 atm = 760 torr = 760 mmHg
1 atm = 14.7 lb/in2 (or psi)

Temperature


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

ºF
-459
ºC
-273
K
0
C 

5
9

 F  32 

F 

9
5

32

212

0

100

273

373

 C  32

K   C  27 3.15

Convert:







Convert 0.875 atm to bar
Convert 98.35 kPa to atm
Convert 740.0 mmHg to atm
45 °F to °C
56 °F to K

The Gas Laws

The Gas Laws
1. Boyle’s Law –
 P-V Relationship
 the pressure of a fixed amount of gas maintained at constant temperature is inversely proportional to the volume of the gas.

The Gas Laws
2. Charles’ Law –
 T-V Relationship
 the volume of a fixed amount of gas maintained at constant pressure is directly proportional to absolute temperature of the gas. The Gas Laws
3. Gay-Lussac’s Law –
 P-T Relationship
 the pressure of a fixed amount of gas maintained at constant volume is directly proportional to absolute temperature of