1. The Behavior of Gases

2. Properties of Gases (Review)
No definite shape
No definite volume
compressible

3. Kinetic Molecular Theory
moving
molecules
well supported ideas

4. Basic Kinetic Theory of Gases
Composed of particles like atoms (ex: He) or molecules like (O2 and CO2)
There are no attractive/repulsive forces.
Lots of empty space!!

5. Basic Kinetic Theory of Gases
2. Particles move in random, constant, straight-line motion.
Move independently of each other.

6. Basic Kinetic Theory of Gases
3. All collisions are elastic meaning that KE is transferred without loss of energy.
No change in kinetic energy.
Gases tend to diffuse towards areas of lower concentration.

7. Gas Pressure
Pressure- force exerted on container walls by particles in a gas
Units used- kPa, atm, Torr, mmHg
STP (Standard Temperature and Pressure) Table A
273 K or 0°C and
101.3 kPa = 1 atm = 760 Torr (mmHg)

8. Factors Affecting Pressure
Amount of Gas (number of moles)
Increasing amount will increase P (and vice versa)
Ex: bicycle tires, car tires
Temperature
Increasing temp. will increase P (and vice versa)
Ex: Tires deflate in winter
Volume
Decreasing volume will increase P, increasing volume decreases P
Ex: press down on a balloon and it pops

9. Pressure and volume have an inverse relationship, if temperature remains constant.
If volume is increased, pressure is decreased by the same factor.

10. Mathematically, the product of PV is constant or PV = k (where k is some constant).
Boyle’ Law
P1 V1 = P2 V2 = P3 V3…

11. Summary

12. Volume and temperature have a direct relationship, if pressure is held constant.
If temperature (K) is increased, volume is increased by the same factor.

13. Mathematically, the relationship of volume divided by Kelvin temperature is constant or V/T = k.
Charles’ Law
V1 /T1 = V2 /T2 = V3 /T3 …

14. Summary

15. Pressure and temperature have a direct relationship, if volume remains constant.
If temperature (K) is increased, pressure will be increased by the same factor.

16. Mathematically, the relationship of volume divided by Kelvin temperature is constant or P/T = k.
Gay-Lussac’s Law
P1 /T1 = P2 /T2 = P3 /T3 …
Pressure

18. Combined Gas Law Equation
P1 V1 = P2 V2
T T2

19. Combined Gas Law Equation
Steps:
Determine which variable (if any) is kept constant.
Cancel those terms and remove them from the equation (Ex: If the question says that temperature remains constant the new equation becomes P1V1 = P2V2).
Plug in values that are given.
Solve for the unknown.
Be sure to always use temperature in Kelvins.

20. Ideal Gases vs. Real Gases
“Ideal gases” behave as predicted by Kinetic Molecular Theory.
Examples: H2 and He
Gases are most ideal at high temperature and low pressure (also have low mass and low polarity).

21. “Real gases” deviate from ideal behavior.
Why?
At low temps, gas particles become attracted to each other (KMT says they are not).
Under high pressure, gases occupy a specific volume (KMT says they don’t).

22. Avogadro’s Law Avogadro’s number: 6.02 x 1023
Simply refers to the quantity of particles found in a mole.
At STP, 6.02 x 1023 particles of a gas occupies 22.4 L.
At STP, 3.01 x 1023 particles of a gas occupies 11.2 L.

23. Avogadro also hypothesized that equal volumes of different gases at the same temperature and pressure contain equal number of particles (or equal moles).

24. Vapor Pressure
In a sealed container, vapor pressure can be measured above a liquid.
Evaporation occurs when some particles from the surface of a liquid escape causing pressure to build up above the liquid (not to be confused with boiling).

26. Factors that Increase the Rate of Evaporation
Heating a liquid (not to boiling point)
Increasing surface area
Create air currents
(blow across the surface)

27. Liquid-Vapor Equilibrium
Some of the gas particles condense and then we find both evaporating and condensing occurs at the same rate.
Rate of Evaporation = Rate of Condensation

28. Related to Boiling
Boiling occurs when the vapor pressure becomes equal to the external pressure.
At normal atmospheric pressure, we call this normal boiling point.

29. Boiling and Attractive (Intermolecular Forces)
Boiling occurs when heat energy overcomes attractive forces between molecules.
The stronger the intermolecular forces, the higher the boiling point.
The weaker the intermolecular forces, the lower the boiling point.

30. Table H Notice, increasing temperature increases vapor pressure.
Line drawn at kPa corresponds to normal boiling point.