Hielo Y Sal

NATURAL ENERGY RESOURCES
E7002B

SALT AND ICE

Luis Ramos Navarro
Francisco Jose Coello Oller

INDEX:
1. Objectives………………………………………………………… Pag. 3
2. Introduction…………………………………………………….. Pag. 3
3. Experimental process……………………………………….. Pag. 5
4.1 Fine salt…………………………………………………….. Pag.6
4.2 Coarse salt………………………………………………… Pag. 7
4.3 Differentsolutes……………………………………….. Pag. 8
4.4 Minimum temperature……………………………… Pag. 10
4.5 Different types of mixed……………………………. Pag. 11
3.6 Problems we have had……………………………….. Pag. 12
4. Development of the process…………………………….. Pag. 12
5. Possible applications………………………………………… Pag. 12
6. Continuation of the study………………………………… Pag. 14
7. Conclusions……………………………………………………. Pag. 15
8. Bibliography……………………………………………………. Pag. 16

1.Objectives
We have been working in a research project, and our objectives are to study the effect of the salt in the snow and search for different possible applications.
To study these objectives we have worked in the laboratory doing different experiments using snow that we took from the Arena Hockey Stadium.
Moreover we have used different types of salt (fine salt and coarse salt) and sugar tostudy the different effects that each one has on the snow.
2. Introduction
Two things happen when ice and water are placed in contact:
* Molecules on the surface of the ice escape into the water (melting).
* Molecules of water are captured on the surface of the ice (freezing).
When the rate of freezing is the same as the rate of melting, the amount of ice and the amount of waterwon't change on average (although there are short-term fluctuations at the surface of the ice). The ice and water are said to be in dynamic equilibrium with each other. The balance between freezing and melting can be maintained at 0°C, the melting point of water, unless conditions change in a way that favors one of the processes over the other.
The balance between freezing and melting processescan easily be upset. If the ice/water mixture is cooled, the molecules move slower. The slower-moving molecules are more easily captured by the ice, and freezing occurs at a greater rate than melting.
On the other hand, heating the mixture makes the molecules move faster on average, and melting is favored.
Adding salt to the system will also disrupt the equilibrium. Consider replacing some ofthe water molecules with molecules of some other substance. The foreign molecules dissolve in the water, but do not pack easily into the array of molecules in the solid. Notice that there are fewer water molecules on the liquid side because the some of the water has been replaced by salt. The total number of waters captured by the ice per second goes down, so the rate of freezing goes down. Therate of melting is unchanged by the presence of the foreign material, so melting occurs faster than freezing. That's why salt melts ice.

In these pictures, we can see that the molecules of ice are more united, and the molecules of water are more separated. In the second picture we can see that there are less molecules of liquid water that arrive to the ice due to the factthat there are a lot of salt molecules.
To re-establish equilibrium, you must cool the ice-saltwater mixture to below the usual melting point of water. For example, the freezing point of a 1 M NaCl solution is roughly -3.4°C. Solutions will always have such a freezing point depression. The higher the concentration of salt, the greater the freezing point depression, until arrive to a minimumtemperature. The freezing point goes down because melting requires heat, and the heat comes from the water, the temperature of the water drops as it uses heat to melt the ice. As more salt is added, the water temperature will continue to drop as long as the solution still contains solid ice.
But won't any foreign substance cause a freezing point depression, according to...