Example 1. Pure-Component VLE Behavior

Let's investigate the pure-component behavior of the two compounds.  Change the overall mole fraction (z) slider to 1.0.  This changes the system to pure component n-pentane, red.  The fluid immediately vaporizes.  Why does the red fluid exist as a vapor at the same temperature that the blue fluid is a liquid?  Now lower the temperature (T) slider to 310 K.  What happens to the velocities of the molecules?  Is the fluid liquid or vapor at this temperature?  You might want to raise T up to 340 K to compare the velocities at two quite different temperatures.  Also try to compare the structure of the gas at the two different temperatures.  Do you see more instances of pairing or clustering at the lower temperature than at the higher temperature?  Can you explain why this happens in terms of the forces between the molecules and the kinetic energy of the molecules?  After observing the system at 310 K, lower the temperature by 1 K, to 309 K. What happens?  Why does the system become entirely liquid?  Isn't it possible to have some liquid and some vapor?  If not, why not?  If so, at what temperature does this occur?  Note that we have isolated the boiling point at this pressure somewhere between 309 and 310 K.  If we had a finer control on our temperature controller, we could better pin-point where the vapor and liquid are in equilibrium.  Note the relationship of the temperature and composition on the Txy diagram.  Explore in the same manner the boiling point of the blue molecules and observe that the saturated liquid and vapor lines on the Txy diagram meet at the same temperature for the two component limits.  Thus, the vapor and liquid phases can only be in equilibrium a single temperature.

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More Examples: Example 2 | Example 3 | Example 4 | Example 5