In liquids, the crystal has fallen apart rendering the substance shapeless. Nevertheless a liquids certain coherence, being held together in a blob by surface tension forces. In the gaseous state, the atoms (or molecules) are far apart and act individually. There is no coherence. To disintegrate a crystal structure, work must be done against atomic forces in order to pull the crystal apart. As this goes on, the solid crystalline substance is said to melt. One way to supply the energy necessary to do the work of melting is to heat the substance.
When heat is used to melt the substance, it does work against the crystalline forces rather than becoming kinetic energy. Therefore the temperature (which is a measure of atomic kinetic energy) does not change while melting goes on, but remains constant at a value called the melting point. If the temperature of a substance is below the melting point, then heating it simply raises its temperature until the melting point is reached. (Formula: Q = CRA T). However, once the melting point is reached, further heating leaves the temperature constant ND starts breaking down the crystal structure.
This continues until all the substances melted. If still more heat is added, the temperature once again starts to -? I s e . To melt a given amount of different substances requires differing amounts of heat because of differences of crystal structure. The amount of heat required to melt unit mass of a substance is called its heat of fusion. The definition can be expressed in a formula as: where: Q is heat quantity in calories L, is heat of fusion in calories/GM m is the mass of the substance melted in GSM In the present experiment, heat of fusion of ice is measured.
Calorimeter Thermometer Balance Set of weights Ice and water Procedure The determination of the heat of fusion of ice uses the method of calorimeter. Recall that in an isolated system, the total energy is constant. Furthermore, heat flows from hotter to cooler bodies. Therefore if we mix warm and cold objects in an isolated system, the heat lost by the warm bodies will equal the heat gained by the cold we proceed as follows: Weigh the dry calorimeter cup. Add a reasonable amount of water. Weigh again. Subtract these valuates get the mass of the water of the water.
Weigh the dry stirrer. Place the cup in the calorimeter and record its temperature with the thermometer. Obtain a reasonable amount of ice at COCO. Make sure the pieces are small to ensure that the inner temperature of the ice is the same as the surface temperature (COCO. But how do you ensure that even the surface is at zero? ) Remove excess water with a paper towel. Insert the dried ice into the calorimeter. Stir gently. Record the temperature of the mixture at short intervals. The temperature should drop rapidly to a minimum and then slowly increase.
