The three phases of matter can be likened to people attending a football or basketball game. When the fans are all seated before the game or standing for the national anthem, they are arranged like the particles in the solid phase of matter. At half-time when the fans get up and mill around in ÒclumpsÓ to go to the refreshment stand or the bathrooms, they are behaving like liquid particles. When the game is completed, the fans leave the sports arena, get in their cars, and head randomly in all directions. They are scattered over a very large area compared to the area which they occupied at the game. In this case, they are behaving like gas particles. Note: If you find that the pipet ruptures before the triple point is reached, try Tygon TM tubing, clamping a 6-in. piece at both ends.

1. Draw a picture of the solid and liquid particles in a container of a substance at its melting point. [The important differences are in the rigidly arranged structures of the crystalline solids and the more loosely arranged liquid particles. At a given temperature, there is no difference in the average kinetic energy of the solid or liquid phase. The major difference at the melting point is that liquid particles possess mainly translational kinetic energy while a major portion of the kinetic energy of the solid particles is vibrational in nature.]

2. Draw pictures of solid particles, liquid particles, and gaseous particles for a particularsubstance. [Thestudentanswersshould showthattheyunderstand the differences among the three phases of matter in bonding, order, and amount of empty space.]

3. Draw a graph of temperature vs. heat input (a warming curve) for water under normal atmospheric pressure. Take the water from solid ice at ­20°C to gaseous steam at 120 °C. [The student graphs should indicate they understand that there are three ÒslantedÓ portions to the graph (kinetic energy changes) and two ÒflatÓ portions to the graph (potential energy changes). If they are more sophisticated in their understanding of this concept, they may also indicate differences in heat capacities of ice, water, and water vapor by controlling the slope of the ÒslantedÓ portions. The differing heats of fusion and vaporizationcouldbeindicated byshowingtheÒflatÓ portionsofthecurve at the phase changes to be different lengths.]



Figure 17. Warming curve for water.

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