Follow

Phase Transitions

  • I4-01: PVT PHASE DIAGRAMS FOR CO2 AND H2O

    I4-01
    Three-dimensional PVT phase diagram models.
    These are carefully labelled, three-dimensional, four-color pressure-volume-temperature phase diagrams for CO2 and H2O .
    I4

    i4-01a

  • I4-02: PVT SURFACE - TRANSPARENT

    I4-02
    Illustrate aspects of phase transitions.
    This is a "generic" phase diagram on which the instructor can write details using various colors of felt tip pens. Projections can easily be seen, and the overall geometry can be observed because the model is transparent.

  • I4-03: LATENT HEAT - ICE TO WATER TO STEAM

    I4-03
    Show latent heat as ice is transformed to water and then to steam.
    A flask is filled to within one inch of the brim with a mixture of water and ice cubes at the freezing temperature of water. The flask is then heated for about 15 to 20 minutes with the burner on high, with the temperature measured by the dial thermometer. If you were to create a plot of temperature as a function of time, it would clearly show that extra heat is required to produce the ice-water and water-steam phase transitions.
    I0

  • I4-11: BOILING AT REDUCED PRESSURE

    I4-11
    Demonstrate that water boils at a lower temperature under reduced pressure.
    Water is boiled in the flask, then heat is removed and the flask is sealed after boiling ceases. Dry ice is packed around the flask, reducing the pressure inside the flask. The boiling immediately resumes.
    I4, I0

  • I4-12: BOILING WATER BY PUMPING

    I4-12
    Demonstrate water boiling under reduced pressure.

    Place a beaker of water in the bell jar attached to a vacuum pump. Turn on the pump and the water will begin to boil. Discuss the necessity of boiling food longer to cook it at higher elevations. Talk about bubble chambers and cosmic rays influencing when bubbles first appear in the liquid.

    Note: Some of this effect is simply from the air dissolved in the water coming out due to the action of the pump.
    I4, FS0

  • I4-13: CHANGE OF STATE OF LN - POPPING CAN LID

    I4-13
    Show the increase in volume which accompanies the transition from liquid to gaseous nitrogen.
    Pour a small amount of liquid nitrogen into a can (typically under 10ml) and install the plastic lid. The liquid nitrogen heats up, changes to a gas, and forces the lid open.
    I4

  • I4-14: CHANGE OF STATE WITH BANG

    I4-14
    Demonstrate that the volume of a gas is much greater than the volume of the same amount of liquid.
    Fill the small flask with liquid nitrogen and place the balloon over the top. As the liquid nitrogen turns to gas its volume increases, ultimately bursting the balloon. This is a change of state with a bang, hee, hee, har, har.
    I4, I0

  • I4-15 CONDENSATION OF STEAM - GALLON CAN COLLAPSE

    I4-15
    Illustrates forces produced by the pressure drop when steam condenses into water
    A small amount of water in the can is heated with the lid off, filling the can with steam. The can is then removed from the hot plate and the lid quickly screwed tightly thereon. Within a few seconds the steam begins to condense, creating a low pressure inside the can. The greater atmospheric pressure outside crushes the can.
    I0, SU14

  • I4-19: CONDENSATION OF STEAM - SODA CAN COLLAPSE

    I4-19
    Surprising demonstration using condensation of steam.
    A soda can with a small amount of water in the bottom is heated until the water boils, filling the can with steam. Very quickly the can is removed from the heater and inserted upside down into a container of cold water. The steam condenses so quickly that the can collapses, as seen in the photograph. This is quite a dramatic demonstration, and gets a good reaction from students.
    I4, I0, SU15

  • I4-31 ICE BOMB

    I4-31
    Demonstrates forces created by freezing water
    A pipe elbow with end caps is filled with water, sealed by tightening the ends, and dropped into a metal container of liquid nitrogen. Within about one minute the water freezes, expanding sufficiently to break the cast iron with a loud crack and a big cloud of vapor.
    I0, I4, SU5, OS6

  • I4-32: FREEZING WATER BY PUMPING

    I4-32
    Freeze water by reducing the ambient pressure.
    Place about four drops of water onto a cellophane "watchglass" in the vacuum chamber as in the photograph at the left. Evacuate the chamber with the vacuum pump. Almost immediately the water will begin to bubble (boil), as seen in the middle photograph below, and within about one minute the boiling will subside and the water will freeze. When the water freezes it is clearly seen to become opaque on the overhead projector screen, as seen in the photograph on the right below. This is a very dramatic demonstration.
    I4, I0

    i4-32ai4-32bi4-32c

  • I4-35: LOWERING THE FREEZING POINT OF WATER USING SALT

    I4-35
    Demonstrate that the freezing point of water can be reduced by putting ice in a salt water bath.
    The temperature of an ice and water mixture is measured with a digital thermometer. Adding salt to the icewater mixture reduces its temperature. The thermometer can be used to stir the mixture. By this technique the freezing point can be lowered as much as 15 degrees celcius.
    I4

    i4-35a

  • I4-51: SUBLIMATION OF DRY ICE - PROJECTION

    I4-51
    Demonstrate sublimation of carbon dioxide (dry ice) from a solid into a gas.
    Place a chunk of dry ice on the plastic sheet, on an overhead projector if desired. As the dry ice evaporates (evaporation sublimation) it becomes smaller but leaves no residue.
    I4, I0

  • I4-52: CARBON DIOXIDE BALLOON ON LIQUID NITROGEN

    I4-52
    Demonstrate condensation sublimation.
    A balloon filled with carbon dioxide gas is held on top of a liquid nitrogen bath. The volume of the balloon decreases for two reasons: (1) the volume of the gas shrinks according to Charles' law, and (2) the boiling point of carbon dioxide is well above that of nitrogen, so the carbon dioxide condenses, forming dry ice powder. The small granules of dry ice, which can be easily seen in the deflated balloon, disappear as the balloon warms up and inflates once again.

    i4-52a

  • I4-61: BINARY PHASE TRANSITION - CRITICAL OPALESCENCE

    I4-61
    Show the behavior of a binary fluid as it passes through the critical temperature.
    A small sealed vial contains the correct mixture of aniline and cyclohexane to form a binary fluid when heated above its critical point, about 95 degrees Fahrenheit. The fluid is heated by hand or using a beaker of warm water. Then the vial is placed in the laser beam. When the fluid cools down to its critical point it breaks into cells, becoming cloudy, and scatters the laser beam chaotically. This is very dramatic because it happens very quickly.

    The photographs above show the scattering of the laser beam by the fluid above the critical point (left), at the critical point, when the cells are beginning to form (center), and well below the critical point, when the fluid is a cloudy mixture of the two individual fluids (right)
    I4, I0, FS1

    i4-61i4-61ai4-61b