1. Kinetic-Molecular Theory of Gases Notes#5

2. increases All particles are in constant motion.
As temperature increases kinetic energy ?
increases
increases
As gas particles move apart the volume ?

3. Point Masses
Gas particles are treated as a point with no volume and no mutual attraction
-this is because they’re so small compared to the distances between them.

4. STP Ideal Gases A theoretical gas with no volume and no attraction.
A series of theories will be studied about ideal gases
-standard pressure of kPa
-standard temperature of 0°C or 273K
-standard conditions are abbreviated
STP

5. Therefore:
Kinetic theory explains properties of gases based on a molecular view.
The assumptions are:
The molecules are in continuous, random motion.
A molecule has negligible volume.
The forces between molecules are negligible.
The average kinetic energy depends on the temperature.

6. Four Gas Law Variables Are:
V = volume
P = pressure
T = temperature
n = number of particles
(Case is important)

7. Units of pressure SI unit is Pascal (Pa)
1Pa = 1 N/m2 derived from force
1atm = 760mm Hg = 760 torr = kPa =14.7 psi
1torr = 1 mm Hg

8. . . . Boyle’s Law Relates volume and pressure
-gas exerts pressure on its container’s walls
-pressure depends on
*number of molecules
*average kinetic energy of the molecules . .
Pressure = P .

9. . . . . . . . . Boyle’s Law Relates volume and pressure
-gas exerts pressure on its container’s walls
-pressure depends on
*number of molecules
*average kinetic energy of the molecules
Plunger applies pressure (now 2P).
-As pressure doubles, volume becomes ½.
-(note the same number of particles now occupying ½ the space) . . . . . . . .

10. Boyle’s Law Boyle’s Law PV=k *P=pressure *V= volume *k=constant
Experiments happen at room temperature(about 25ºC.) We need to convert the results to STP.

11. Boyle’s Law
Since and
then (substituting for k)

12. Boyle’s Law
Since and
then (substituting for k) or

13. Boyle’s Law Since and then (substituting for k) or Units
pressure - kPa
volume - cm3

14. Problem: a gas is collected in a 242 cm3 container at 87. 6 kPa
Problem: a gas is collected in a 242 cm3 container at 87.6 kPa. What is its volume at STP?
V1= P1= V2= P2=
242 cm3
87.6 kPa ?
kPa
Think: pressure goes from 87.6 kPa to kPa so Volume should be________ than 242 cm3
Math:

15. so
Note: 209 < 242cm3
Now do CMC 358: 1, 2, 3(a,c,e) and 4(a,c,e).