When you are ready to activate the animation click the start button in the animation rectangle.

When the animation begins notice what is happening to the particles. You should also notice what is happening to the temperature of the system as indicated by the thermometer. When the temperature stops changing click the mouse on the Continue button and the animation will continue. When the animation finally stops answer the questions. It is OK to view the animation more than once, just click on the Repeat button.

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. Briefly describe what you observed happening when you ran P-L Exploration #1. Use any or all of the following terms in your explanation: gas, liquid, solid, particles, attraction(s), temperature, kinetic energy, translational energy, speed, chemical change, physical change, condensation, freezing, melting, vaporization, collision.

Expert: Initially the substance is in the gas phase. The particles have high kinetic energy and are well separated in space. As the temperature drops the speed (translational energy) of the particles decrease. At the lower speeds collisions between particles are not as elastic, that is, they seem to stick together when they collide. The particles stick together because the attractive forces between the particles become more important as the particles slow down. As the temperature drops further the particles stick together and eventually fall to the bottom of the container. The particles form a liquid, when all of the particles are at the bottom of the container, but still moving relative to each other. Finally at the lowest temperature the particles stop moving relative to each other and form a solid. The sytem undergoes phase changes (physical change) as it moves from gas to liquid to solid. When the sample is heated the reverse occurs.

2. List any phase changes you observed in the animation. Indicate if you think each phase change is exothermic or endothermic.

Expert: The observed phase changes as the sample cooled where; gas to liquid and liquid to solid. These two phase changes are exothermic. To go from gas to liquid or from liquid to solid heat must be removed. When the sample is heated the phase changes are solid to liquid and liquid to vapor. This direction the phase change is endothermic. Heat must be added going from solid to liquid or from liquid to vapor.

3. List any phase changes you did not observe in the animation.

Expert: Sublimation (solid to gas) and deposition (gas to solid) were not observed in this animation.

4. Are there any questions you would like to ask about the animation?


Translational energy is energy of motion.

The particles come together at the bottom of the container as opposed to being completely separated because of the attractive forces between them.

Exothermic is the term we use to describe the flow of heat from the system to the surrounding. When a gas condenses the excess heat must be removed from the gas (removed from the system), so that process is exothermic.

Endothermic is when heat is added to the system from the surroundings. Heat must be added to liquid water (added to the system) to convert it to the gas phase.

When the particles are heat sufficiently to attain the gas phase any additional heat causes the particles to move faster (increases their translational energy.) and that is all. So the sample remains in the gas phase.

Adding cold, or removing cold? No we do not use those words in that way. We add or remove heat. To cool something (remove heat) we place the system we wish to cool in a surrounding that is at a lower temperature. Than heat will flow from the system to the surroundings (exothermic).

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