Temperature Curves Lab

Heating and Cooling Curves

Introduction: Experiments 6 and 7 were concerned with the exchange of heat between a substance and its surroundings when the substance undergoes a change in phase. This transfer of heat was indicated by measuring its effect on the temperature of the surroundings (the water in a calorimeter). No direct measurements of the substance undergoing change were made. In this experiment you will observe, by direct measurement, the effects of cooling and heating a pure substance. In Part I, a pure substance will be cooled (heat removed) at a constant rate. Starting with a substance in is liquid phase at a temperature well above its freezing point, temperature readings will be made at regular intervals until the substance

While heat is added at a constant rate, temperature readings will be made until the substance is in its liquid phase at a temperature well above its melting point. The data collected in Parts I and II will be used to construct a graph, which will consist of two curved lines - a cooling curve and a heating curve. When completed, the graph will show pictorially what happens to a pure substance as its temperature is raised and lowered over a temperature interval that includes its freezing and melting points. The graph will also show how the freezing and melting points of a substance are

Endothermic?

Freezing, condensing, and deposition are exothermic. This is due to the fact that a substance must lose energy in order to have a phase change. The loss of energy allows the molecules to travel slower, where they get closer and closer to one another. Melting, vaporization, and sublimation are endothermic. This means that the molecules must absorb energy to go through this phase change. The energy gained speeds up the molecules so that they are eventually spaced enough to change phase. In which phase of a substance do its particles have the greatest average kinetic energy?

Particles have the greatest average kinetic energy in the gaseous phase. The particles are spaced out and have more room to move around, but still collide with one another. Ideal collisions are elastic, meaning that two colliding particles do not lose energy when they hit, but rather bounce back with the same amount of energy. The speed and energy of these particles allow for the gaseous phase to have the greatest average kinetic energy compared to other