The animation is already running after loading. Watch the animation for a minute and then review the questions. After reading the questions you can click either the Evaporation or the Vapor Pressure button. The animation should continue to play once started.

Important do not press the enter key or the Return key while you are answering these questions. Your Browser will interpret either key the same as clicking the mouse on the Submit button. So BE CAREFUL!

Give me some responses to the questions below and I'll give you some extra credit.


Laboratory Section:

1. Before clicking the Evaporation or the Vapor Pressure button, briefly describe what you see happening.


I see particles (represented as red spheres) moving rapidly. All of the particles are in a confinded space and do not fill the container. There is very little space between particles. There must be some attractive forces between the particles becasue even with the rapid movement all of the particles stay close to one another.

2. What phase is represented in the animation? Briefly support your answer with an explanation that lead you to the phase you chose.


The phase is condensed since the particles are only at the bottom of the container. Since the particles are moving, are not in fixed, static positions, the phase is liquid. Liquids adopt the shape of their container and the particles are very closer to each other, that is, very little space between particles. The particles are in constant motion, but the attractive forces are sufficient to keep the particles close to one another. The very little space between the particles means liquids are not very compressible. The constant, rapid motion of the particles is what gives rise to the ability of liquids to flow.

3. When you click on the Evaporation button what happens that differs from what was happening before clicking that button.


Before clicking the Evaporation buttons the particles remain in the liquid phase. When the Evaporation button was clicked all of a sudden a particle in the liquid phase escapes into the vapor phase. For a particle, initially attracted to other particles around it, to escape into the gas phase several things must happen.

1. the particle escaping must be on the surface of the liquid;
2. the particle must have sufficient energy to overcome the attractive forces of the particles around it, holding it in the liquid phase;
3. the particle must be going in the right direction so they escape out of the liquid.

4. When you click on the Vapor Pressure button what happens that is different from what was happening before clicking the button.


After clicking on the Vapor Pressure button a lid is slid over the top of the container confining the particles in the gas phase. As particles are able to escape the liquid phase into the vapor phase they remain above the liquid. So after a brief time the substance is clearly in two phases, gas and liquid.

5. After clicking the Vapor Pressure button, observe the behavior for a minute or two and describe what seems to be happening.


As more paricles evaporate a point is reached where the rate of evaporation is equal to the rate of condensation. That is, everytime a particle evaporates another particle condenses so the number of particles remain constant above the liquid. We say the vapor is in equilibrium with its liquid.

6. How would you define vapor pressure after watching this animation? (Do not look this term up in your book, just go for it based on the animation.)


Vapor pressure must be related to the pressure of the vapor above its liquid. Vapor pressure is defined with three slightly different definitions;

1. the pressure exerted by the vapor, above a liquid at a particular temperature;
2. the pressure exerted by the vapor when the rate of condensation equals the rate of evaporation;
3. the maximum pressure, exerted by the vapor, above its liquid at a given temperature.

7. Is there anything about this animation that you feel you do not understand? List your concerns/questions.