1. The Nature of Liquids
Chp 10

2. The Nature of Liquids:
Like gas particles, liquid particles are also in motion
Unlike gas particles, liquid particles are attracted to each other

3. Intermolecular Forces:
1. Reduce the amount of space between liquid particles
2. Particles do not have sufficient amount of kinetic energy to overcome these forces
3. Therefore, they cannot escape to the gaseous state

4. Intermolecular Forces:
Intermolecular forces are the reason why liquids are more dense than gases
Liquid
Gas

5. Evaporation:
Conversion of a liquid to a gas or vapor, at the surface of the liquid
Does not a require certain temperature or pressure
How?

6. I have lots of kinetic energy
H2O
I can fly!
H2O
H2O
H2O
I do not have lots of kinetic energy

7. Evaporation:
How?
Some particles have enough energy to break away
Some collide with air molecules and bounce back into the liquid

8. Evaporation and Heat:
Increase the temperature = increase in averaged kinetic energy = increase in rate of evaporation

9. I’m not crazy your crazy
Evaporation:
Evaporation is a cooling process!!
Particles with highest energy escape first!
You must be crazy??
I’m not crazy your crazy

10. Evaporation:
The liquids temperature decreases because there is a lower average kinetic energy of the particles left behind!!

11. You have probably experienced evaporation:
Perspiration
Water molecules absorb heat from your body and evaporate from your skin’s surface

12. Vapor Pressure: Evaporation of a liquid in a closed container
Particles vaporize and collide with the walls of the container creating vapor pressure
Vapor pressure = force due to the gas above the liquid

13. As time moves on, more particles vaporize
Vapor Pressure:
As time moves on, more particles vaporize
Some will condense back into the liquid
Eventually equilibrium will be reached between vapor & condensed particles

15. Vapor Pressure and Temperature:
Increase in temp. = increase in vapor pressure
Because of increased kinetic energy
Particles are colliding with greater frequency

16. Manometer:
Device used to measure vapor pressure
Figure 10.9 illustrates a manometer

17. Boiling Point:
The temperature at which the vapor pressure of the liquid is equal to the external pressure

18. If external pressure changes, the boiling point will change
Example: Bell Jar experiment
Lowered the pressure
Water boiled at a lower temperature

19. Boiling Point:
The higher the elevation = less pressure = the lower the boiling point
There is less pressure pushing down on the liquid, therefore it is easier for the particles to escape!
Water boils at 95o C in Denver

20. Boiling Point
If we stood on the moon, we could boil water in our hands
The atmospheric pressure on the moon is very low, therefore water boils at a much lower temperature

21. Look! I can boil
Water in my hand

22. How does boiling differ from evaporation? How are they similar?
Thought Questions:
How does boiling differ from evaporation?
How are they similar?
Is boiling also a cooling process?

23. Now, go on to The Gaseous State Power Point
Click Here
to go on to
The Gaseous State