This SIR allows a lecturer to involve the class in an exploration of liquid-vapor equilibrium. Several facilities are provided. The first, which appears immediately on entry to the SIR, is discovery of the way water evaporates (boils) and condenses.
Discovery
The
initial display shows a test tube partly filled with water, and a pressure - temperature
diagram. You may click the mouse anywhere on the diagram. The computer responds with the
behaviour of water appropriate to that temperature and pressure: evaporation (bubbles rise
up through the liquid) or condensation (drops run down the sides of the tube).
The pressure and temperature at the chosen point are displayed above the test tube. After each animation, a red star for evaporation or a blue circle for condensation records the behavior at that point. Several such points define a low-pressure, high-temperature evaporation region and a high-pressure, low-temperature condensation region. You may then insert the vapour pressure curve, which separates them.
Two closely related displays accessible using the menu bar are Const P (constant pressure) and Const V (constant volume). The screen layout corresponds to that of the discovery display, but the vapor pressure curve is present from the start. You may click anywhere on the screen and get the appropriate behavior, but the red and blue points no longer persist on the screen. These displays illustrate what will actually happen in the real world, under different conditions.
Vapour Pressure of Solvents allows you to compare the v.p. curve of water to that of one of six solvents. You may click on the graph to move a crosshair, and see the temperature and pressure at the point, in order to compare volatilities, boiling points, etc.
The Humidity facility shows the vapor pressure curve of water from -10° to +35° in greater detail. The solid-liquid line is also shown, so you can see that ice also has a vapor pressure. The change in slope of the vapor pressure line at the triple point is there, but it is hard to see. This graph can be used to read vapor pressures for relative humidity calculations. A double crosshair facility allows marking of the vapour pressure at two different temperatures.
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Updated July 17, 2000