2. The Property of Gases – Kinetic Molecular Theory
And Pressure

3. Kinetic Molecular Theory of Gases
The word kinetic refers to motion.
Kinetic energy is the energy an object has because of its motion.
Kinetic Molecular Theory makes assumptions about:
Size
Motion
Energy of gas particles

4. Kinetic Molecular Theory Part 1
According to the KMT all matter consists of tiny particles that are in constant, random motion
Move in a straight line until they collide with other particles or with the walls of the container.

5. Kinetic Molecular Theory Part 2
2. Gas particles are much smaller than the distances between them. Most of a gas consists of empty space.
Gas consists of small particles that are separated from one another by empty space
Most of the volume of a gas consists of empty space
Because they are so far apart, there are no attractive or repulsive forces between the gas molecules
The motion of one particle is independent of the motion of other particles

6. Kinetic Molecular Theory Part 3
No kinetic energy is lost when gas particles collide with each other or with the walls of the container (elastic collision)
Undergoes elastic collision – no kinetic energy is lost when particles collide.
The total amount of kinetic energy remains constant.

7. Kinetic Molecular Theory Part 4
All gases have the same average kinetic energy at a given temperature
Temperature is a measure of average kinetic energy of particle in a sample of matter.
Kinetic energy and temperature are directly related
The higher the temperature, the greater the kinetic energy
The Kelvin temperature of a substance is directly proportional to the average kinetic energy of the particles of the substance _____oC = _______Kelvin
There is no temperature lower than 0 Kelvin (Absolute Zero).
Kinetic Energy = ½ mv2; where m = mass and v = velocity

8. Absolute Zero
The greater the atomic and molecular motion, the greater the temperature is of a substance.
If all atomic and molecular motion would stop, the temperature would be at absolute zero (0 Kelvin or -273 oC)

9. Diffusion and Effusion
Diffusion – describes the movement of one material through another
Particles diffuse from an area of high concentration to low concentration
Effusion – gas escapes through a tiny opening.
The heavier the molecule, the slower it will effuse or diffuse

10. Diffusion and Effusion

11. Pressure Pressure is the force per unit area
Gas pressure is the force exerted by a gas per unit surface area of an object.
Gas pressure is the result of billions of collisions of billions of gas molecules with an object
Atmospheric pressure (air pressure) results from the collisions of air molecules with objects.
The air pressure at higher altitudes is slightly lower than at sea level because the density of the Earth’s atmosphere decreases as elevation increases.
Vacuum - Empty space with no particles and no pressure

12. Measuring Pressure
Barometer – an instrument used to measure atmospheric pressure

13. Measuring Pressure
Manometer – an instrument used to measure gas pressure in a closed container

14. Units of Pressure and STP
Average atmospheric pressure is 1 atm
1atm = 760 torr = 760 mmHg = kPa
STP (Standard Temperature and Pressure)
1 atm and 0oC or 1 atm and 273 K
S T P e n e r f c t
Like using the our system of measuring versus the metric system; means the same thing but different units

15. Dalton’s Partial Pressure
Dalton’s law of partial pressures states that the total pressure of a mixture of gases is equal to the sum of the pressures of all the gases in the mixture.
Ptotal = P1 + P2 +P Pn

16. Conversion Factors for Pressure
1 atm = 760 torr = 760 mmHg = kPa

17. Example 1 Convert 2.5 atm into torr, mmHg, kPa 2.5 atm 760 torr 1 atm
2.5 atm 760 mmHg
1 atm
= 1900 mmHg
2.5 atm kPa
1 atm
= 250 kPa

18. Example 2 Convert 215 kPa into torr, mmHg, atm 215 atm 760 torr
215 atm 760 mmHg
101.3 kPa
= 1610 mmHg
215 atm 1 atm
101.3 kPa
= 2.12 atm

19. Dalton’s Law of Partial Pressures
Ptotal = P1 + P2 + P3 … + Pn

20. Example 1 Ptotal = PO2 + PCO2 + PN2
0.97 atm = PO atm atm
PO2 = 0.15 atm

21. Example 2 Ptotal = PO2 + PCO2 + PCO
**You first have to put everything in the same units!
Ptotal = PO2 + PCO2 + PCO
235 kPa 1 atm
101.3 kPa
= 2.32 atm
455 torr 1 atm
760 torr
= atm
Ptotal = atm atm atm
Ptotal = 3.48 atm

22. COCl2

23. C2H2AsCl3

24. Cl3CNO2

25. C4H8Cl2S