Chapter 10

Part 2

Vapor Pressure and Boiling Point

James Prescott Joule

Demos to Prepare:

Vapor Pressure & Boiling Point
The Flask, aspirator, Hg manometer.
Measure the VP of H2O at different temps.
Discover The 15 Shocks of:
Boiling without heating
Two ways to boil
The 70oC coffee test on Pikes Peak
Super heating by pressure
Cooling by boiling (with vacuum)
The Sizzle (collapsing bubbles}
Boiling by cooling (condensation)
Freezing by boiling (extinguisher)
Wet things and the Wind-chill
Crashing bubbles in the cold tube
The Great Suckback!
Love Meter!
Sling Psychrometer to measure humidity
The  Geyser!
Capacity of Air & Humidity
Four-liter jug  and aspirator.
Ice block, wire & weights.
Iodine crystals.

Equilibrium is reached in a closed system when
the rate of evaporation equals the rate of condensation.

Gas Model demos, Video:

Super Heated Steam is awesome! Video:

Freezing by Boiling!

Superheated water (200oC) under high pressure (30kg/cm2) expands explosively when the pressure is released. The heater rockets 170 meters high! Video:

We can have a superheated liquid at room temperature (20oC) like the CO2 in a fire extinguisher. Liquid CO2 at 20oC has a vapor pressure of 100 atmospheres (100 kg/cm2! To contain that we need a strong steel container. If the valve is broken off, the awesome flashing of liquid to gas makes the cylinder into a rocket that can penetrate a wall! Video:

After steam cleaning, the tanker was sealed up.
The steam condensed to water leaving low pressure inside!
1 kg/cm2!

Crushing cans and steel barrels by condensing steam. WOW! The steam condenses about 1500 times going from Gas to Liquid. This huge reduction of pressure inside the can allows atmospheric pressure ( 1 kg/cm2) to smash the can and barrel. Video:

Duckie's head is cooled by the evaporation of water in the wet fabric. So the vapor pressure is lower at the top. The vapor pressure in the warm rump is greater causing the fluid to rise up in the neck of Duckie. This causes Duckie to tip over and dump the fluid back into his lower regions.

In the Franklin Love Meter, warm fingers (37oC) raise the vapor pressure causing the liquid to rise up and bubble at the top.

Boiling nitrogen demos, Video:

The Sling Psychrometer Measures Relative Humidity

Regelation of Water

Pressure melts the ice and it refreezes when the pressure is released.
Ah... The Principle of le Chatelier.

e.g. Ice Skating, Nasty Snow Ball, Glacier Movement

Raising the earth’s average temperature by 0.3oC will cause the
melting of the glaciers. The oceans will rise 100 meters!
Bad news for most major cities on earth. And to the highlands to
which all of those people will be fleeing.

Just a 4Co increase in average temperature!

Sublimation of Dry Ice and Iodine
They change from solid <---> gas
Skipping the liquid state.

Here Endeth Heat Part 2

Go to Heat Part 1