 A “model” is an approximation that attempts to explain observable behavior, allows for future predictions in experimentation.
 Based on behavior of individual gas particles: (atoms: Ne,He ; molecules
H2,Cl2,CO2)

 4 Postulates
1. The volume of individual particles is assumed to be negligible (zero).
2. The Particles are at great distances from each other – between them, empty space.
3. The particles are assumed to exert no forces on each other, nor do they attract or repel each other.

4. The average KE of a “collection” of gas particles is assumed to be directly proportional to Kelvin.
 ***This model works only for ideal gases***
 Real Gases do have volume, they take up space, and they do exert forces on each other b/t them (melting/boiling)
 We use Ideal gases + their behaviors in Chem. 1

1.
The Kelvin Scale:
- An index of gas motion
- NOT a measurement of heat
2. T, temperature is directly proportional to KE, kinetic energy, energy in motion.
- heat a gas sample T ^, KE ^, motion ^

- “absolute zero” – 0K – all motion stops
- a gas sample at 100K has half the
KE of a gas sample at 200K
- K = Degrees Celsius + 273
- 273K is standard temperature

1.
2.
3.
Individual gas particles exert a force on the side of their containers (balloon).
Atmospheric Pressure: Gravity pulling particles
Atmospheric pressure can change with altitude, greater elevation, less pressure, less gas molecules

 Kinetic Theory works for IDEAL gas behavior – theoretical for almost all situations of T + P
 Remember! T – in Kelvin, measure of
KE of gas particles

 Remember… Kinetic theory asserts 2 assumptions about gas particles.
1. Gases have no volume, REAL gases do, they are matter therefore they take up some space, though very little.
2. No attractive forces exist b/t gas molecules, but REAL gases do have them, otherwise how could they take condense back to the liquid state.

1 ATM = 760 mmHg = 760 torr = 101.3 KPa



ATM= atmospheres mmHg= millimeters of mercury
Torr= Torricelli's

KPa= kilo Pascal's
Ex: convert 9.23 atmospheres of pressure to KPa
9.23 atm x 101.3 KPa = 9.35 x 10 2 KPa
1 atm
Ex: 99.2 KPa to mmHg
99.2 KPa x 760 mmHg = 744 mmHg
101.3 KPa

 Dalton’s Law of Partial Pressures -
P
Total
= P
1
+ P
2
+ P
3
+ …. + P at a constant T and V
8
The total pressure exerted by a mixture of gases is the sum of the partial pressure of each gas.


Air is a mix of gas. The partial pressures are: PN
2
593.4mmHg, PCO
2
=
= 0.3mmHg, Pothers= 7.1mmHg, oxygen is also a component. Calculate partial pressure of oxygen at a barometric pressure of 1 atm.

 Boyle’s Law for Pressure – P
1
V
1
=P
2
V
2
Constant Temperature, an inverse relationship b/t P + V, as P increases
V decreases and vice versa.


P1V1 = P2V2
Example) A 153 cm 3 sample of N
2 gas originally at a P of 82.34 KPa will occupy what volume at standard pressure?

 Charles Law for Temperature –
Volume Changes
V
1
= V
2
T
1
T
2
Constant P, a direct relationship b/t V +
T, as V increases, T must also increase and vice versa. T in Kelvin (can’t have a negative volume or motion)

V
1
= V
2
T
1
T
2
Example) A balloon has a volume of 98 cm 3 on a 32 C day. If the temperature the following day is 48C, what is the volume?

 Guy-Lussac’s Law for Pressure –
Temperature Changes
P
1
= P
2
T
1
T
2
Constant V, a direct relationship b/t P + T , as one increases/decreases so does the other

 Combined Gas Law: P
1
V
1
= P
2
V
2
T
1
T
2
• Ideal Gas Law: PV=nRT or gRT/FM

 P
1
V
1
= P
2
V
2
T
1
T
2
Ex) A sample of diborane gas, B
2
H
6
, a substance that bursts into flame when exposed to air, has a P of 345 torr at a T of -15C and a V of 3.48 L. If conditions are change such that the T is 36C and the P is 0.616 atm, what will be the V?


PV=nRT n=# of moles
How many moles of Argon gas can be found in a cylindrical light tube with a volume of 3.7 L and a under a pressure of 162 KPa. The T in the tube is 350 K.


PV= g (R)(T)
FM
Ex) How many grams of carbon dioxide are in your lungs at a T of 37C and under a pressure of
768 mmHg. Your lung capacity is 4.8 L.


PFM = g = d
RT V
Ex) Calculate the density of NO2 at 300K if its under a P of 6 atm in a 5.0 L container.