Dry 3 - Liquids and Solids (cont.).docx - Dry 3 Liquids and...

This preview shows page 1 - 3 out of 5 pages.

Dry 3 Liquids and Solids (cont.) Introduction In this lab set we will finally get to the nitty-gritty of phase changes and the relationship of these processes to heat energy. We can now start to understand what heat is. In the first procedure we will observe the response of temperature as heat is pumped into a system (ice/water/steam). Heat is a form of energy. It manifests as temperature differences, but it is not temperature. It always moves from a higher-temperature body to one with a lower temperature. Most of the time it results in an increase in molecular motion, whether in solids, liquids or gases. Temperature is a measure of molecular velocity. Heat is the total ensemble of molecular motion in a body. In part 1 you will follow the temperature changes as water goes through its three phases. At first you will cool down some water by adding ice. Then you heat up the water until it reaches its boiling point of 100 C at atmospheric pressure. Then the molecules don’t move any faster. Instead,, the heat you add gets shunted to breaking the bonds between molecules- with the molecules staying in pretty much the same place as they were before. The vibrational motion gets shunted to changes in the configuration of the electrons in the liquid. Then, when all the molecules have become independent, the resulting vapor transforms the heat into molecular motion and the temperature again rises. Cooling involves exactly the opposite processes- when you cool down steam (extract heat) the molecules slow down until the molecules are moving slow enough that they start sticking to each other. After they are all stuck together (water) any heat removal is manifested by reduced velocities until they are slow enough that they stick together even more (ice). After they are frozen together, further heat removal results in slower crystalline vibrations. Sometimes people say that condensation and freezing “give off” heat. This is misguided in the case of spontaneous heat transfer. Heat is never “given off” in such situations. It is pulled off by a colder thing. Similarly, heat is not really “extracted” by fusion or boiling. It is supplied from the surrounding environment. Refrigerators/air conditioners/heat pumps at first may appear to break this rule- and they do. These devices operate by adding in extra energy that gets transformed into entropy in the course of their heating-cooling cycles.
In the first experiment you prepare an ice sample in a calorimeter and pump in heat, tracking the temperature through the various stages. The second experiment is a little different. It is mainly an introduction to crystal structure theory. It gives you a taste of how molecules or atoms arrange themselves into a

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture