1. Surface Tension and Hydrogen Bonding
Phase Changes
Surface Tension and Hydrogen Bonding

2. Phase Change of Water Temperature (C) Time (min) 110 100 90 8070 60 50 40 30 20 10
-10
Water Boiling
T = Constant
Temperature (C)
Water Heating
Temp = Rising
Temperature is constant during a phase change. Normally adding heat energy to something will increase its temperature as the molecules move faster. During a phase change the energy is used not to make the molecules move faster but to break the chemical bonds holding them together.
Ice Melting
T = Constant
Time (min)

3. Why are steam burns worse than water burns?
Energy vs Temperature
110
100 90 80 70 60 50 40 30 20 10
-10
Gas
Liquid Boiling
Temperature(C)
Liquid Warming
Why are steam burns worse than water burns?
In order for liquid water to turn into a gas (steam) you have to add a lot of extra energy to it. When hot steam hits your skin all the energy from the steam is released onto your skin as the steam cools to the same temperature of your skin (thermal equilibrium). Remember heat always transfers from hot to cold. All this extra heat is called latent heat.
Turning a liquid into steam takes a LOT of energy and the opposite is true. Going from steam to a liquid (condensation) releases all this energy.
Solid Melting
Solid Warming
Heat Energy Added (J)

4. Energy vs Temperature Temperature(C) Heat Energy Added (J) 110 100 9080 70 60 50 40 30 20 10
-10
Temperature(C)
Energy Released by water!
Energy Absorbed by water
Heat Energy Added (J)

5. Draw a Phase Change graph of Heat (y-axis) vs Temperature (x-axis).
During Condensation energy is_______ by water?
During evaporation energy is ________ by water?
During melting energy is __________ by water?
During freezing energy is __________ by water?
Why is evaporation called a cooling process?
What is latent heat of vaporization?
What is latent heat of fusion?
DEPOSITION: Condensation and Freezing: Released
SUBLIMATION (SOLID TO GAS) Evaporation and Melting: Absorbed by water
Evaporation cools you because to evaporate the energetic water in your skin (which absorbed energy) is released. Your body is releasing energy which means you have less (you cool off through sweating).

6. Water is A Polar Molecule!
Why does water have such a high latent heat? Why is so much energy released or absorbed?
Water is A Polar Molecule!
Water has a + side and a – side!

7. N S N S + - + N S N S - Electrical Charges are like tiny magnets.
Opposite Charges Attract ( + and - )
Like Charges Repel ( + and + or - and - ) + -
Opposites Poles Attract
Like Poles Repulse + N S N S
Show magnetism demo -

8. O H O O H H - Water Molecules are attracted to one another! +
During a phase change the energy is used not to move the molecules but first to break the chemical (hydrogen) bonds holding the water molecules together! O H + O H - O H
HYDROGEN BONDS Require energy to break!

9. Water as a Polar Molecule
Phet Water Simulation
Perform Polarity mini-Lab
Introduce Water as a polar Molecule….to explain the bonding and lattice structure…
Watch Closely.
Surface Tension Demo and Paper towels.

10. SURFACE TENSION: Hydrogen bonding is stronger at the surface.
A water strider uses the high surface tension of water to walk on its surface.
“A molecule within the bulk of a liquid experiences attractions to neighboring molecules in all directions, but since these average out to zero, there is no net force on the molecule. For a molecule that finds itself at the surface, the situation is quite different; it experiences forces only sideways and downward, and this is what creates the stretched-membrane effect.”
Via Chemwiki

11. Violating Kinetic Theory: Polarity of water
What happens if you put a can of soda in the freezer and leave it there?
Shouldn’t it contract (get smaller) as it cools?
Why does it expand and explode?
Actually do it.

12. Density Decreases as Temperature Increases
Density Increases as Temperature Decreases
Substances Expand when Heated
Substances Contract when Cooled
T↑ V↑ D↓ T↓ V↓ D↑
Did Mr. Sapone Lie?
Ice is colder than water so shouldn’t it be more dense?
Does Ice Sink in water?
ICE CUBE

13. Water behaves different but only in this range! (32F-40F)
This is important for life as we know it on earth and explains why soda explodes in the freezer!
100°C
Naked Science Video
PHET SIM
Water at 4°C will EXPAND when cooled until 0°C at which point it becomes ice.
Likewise, as Ice at 0°C melts it CONTRACTS as it turns into a liquid.
Water expands when heated
Water contracts when cooled
4°C
Water behaves different but only in this range! (32F-40F)
0°C
Water in pipes freezing, frost wedging and mechanical erosion, lakes not freezing over totally and al fish dieing disrupting the foodchain, landscape of the world changing as there would be no polar ice caps
Water expands when heated
Water contracts when cooled
-10°C

14. Water as a Polar Molecule
Phet Water Simulation
Perform Polarity mini-Lab
Introduce Water as a polar Molecule….to explain the bonding and lattice structure…
Watch Closely.
Surface Tension Demo and Paper towels.

15. Penny Drop Data
Student
# Drops
J. Medina
73?

16. Defenitions Cohesion Adhesion Surface tension Capillary action (link)
Hydrogen Bond
Intermolecular forces
Why does a meniscus form in a graduated cylinder?