Thermodynamic Variables of KNO3

Topics: Thermodynamics, Solar energy, Temperature Pages: 6 (1541 words) Published: October 12, 2013

Experiment 3:
Solution Calorimetry: Thermodynamics of Potassium Nitrate

II. Abstract
A determination of thermodynamic variables of KNO3 is presented. KNO3 was heated and dissolved in varying volumes of distilled water. Upon dissolution, the KNO3 solution was removed from heat and the temperature was recorded once crystals formed. For each solution, ∆G the Ksp were found with the temperature and molarity values. ∆H and ∆S were found through the linearization of the data with a plot of lm(Ksp) vs. . ∆G becomes increasingly negative as temperature and concentration increased. ∆H was found to be 29.46 kJmol-1 with a 15.7% error compared to literature values. ∆S was found to be .120kJmol-1K-1 with a 3.81% error compared to the literature value.

III. Introduction
Potassium Nitrate is a molecule of many applications. Potassium Nitrate is applied in explosives, production of glass, and in solar power plants. There are many industrial applications in explosives, the production of glass and has recently been applicable in solar power plants. Potassium Nitrate is able to assist in one of the largest problems with solar power, which is the storage of solar power once it is collected. The solar power industry has long been concentrated on developing photovoltaic cells, but recently plants call Concentrating Solar Power (CSP) plant have found new methods involving KNO3 for energy1. With KNO3 as such a promising source of energy, its thermodynamics whilst in solution are of interest. The thermodynamic properties of the molecule need to be understood so that its uses for creating green energy can be improved upon. Beyond energy for buildings, potassium nitrate can also have a hand in the energy in the human body. When consuming food, there is hope that the food is free of chlorine and other unwanted metals; thanks to potassium nitrate, that is a real option. Potassium and nitrogen are elements essential to the life cycle of the plant. Previous sources of these elements consisted of chlorine containing substances, which would introduce that chlorine into the plants. Applications of potassium nitrate in fertilizers have removed the necessity of metals being introduced into crops. Potassium nitrate does not simply allow farmers to keep metals out crops, but also to increase crop yield and plant health. When potassium nitrate is in solution it is able to offer plants a source of potassium and nitrogen, two elements essential to plant growth and health, without any negative effects1. This exhibits another instance in where the spontaneity of the reaction would be of great interest. If the reaction is spontaneous, the use of potassium nitrate in fertilizers is a useful application. If not, then adjustments would need to be made accordingly.

The thermodynamics of a solution will help further applications of KNO3. When studying thermodynamics there are three variables that stand prominent: ∆G, ∆H, and ∆S. ∆G represents the amount of free energy of a system, which is ideally minimized and less than zero for spontaneous reactions. ∆H is the enthalpy or the total measure of the energy of a system. ∆S is the entropy and represents the amount of disorder found in a system. These thermodynamics variables are related through the equation ∆G=∆H-T∆S.

A solution of KNO3 and water is created and allowed to cool until crystals are first observed, which is when the reaction is at equilibrium. The values of molarity and temperature are recorded and used to calculate Ksp and ∆G. ∆H and ∆S are found through a plot of ln(Ksp) vs. . The values obtained will be compared to the literature values.

IV. Experimental Procedure
A 400mL beaker was half filled with tap water and boiling ston, placed on a hot plate, and heated. A ring stand was assembled to submerge a half of a 25x 200mm test tube in water. The test tube was filled with 20.006 g of solid KNO3 and 15 mL of distilled water. At the point where...
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