CHM-106: Lab Exercise 29 Thermodsnamis of an Kauilibrium Salution Lab Exercise 5

Question

CHM-106: Lab Exercise 29 Thermodsnamis of an Kauilibrium Salution Lab Exercise 5 in CHM-105 dealt with the heat of dissolution of various compounds dissolved in water. The compounds. The science of thermodynamics, however, is much more than simply calculating heats of dissolution. As part of your studies in CHM-105, you learned about enthalpy (E), entropy (S and Gibbs Free Energy (G). You may recall that these three factors are related by the equation AG-AH-TAS. In addition, G is related to the absolute temperature (%) by the equation: G= RT Inf, Kspis the solubility product, similar to the equilibri will delve more into these concepts. equation, Q = mcAT, allowed you to determine the Heat of Dissolution of the um constant. Today's exercise Potassium nitrate (KNO,) is a strong electrolyte whose solubility in water varies with temperature. The dissolution reaction is: The equilibrium is established when the amount of KNO, dissociating to ions is equal to the anount of ions that associate back to KNO>. Changing the dissolution temperature can alter the equilibrium point. In the laboratory, the reverse of this phenomenon can be demonstrated by varying the concentration of KNOs and measuring the equilibrium temperature with a thermometer. In other words, if we know the concentration of potassium nitrate in solution and the temperature where crystals and ions are in equilibrium, we can calculate factors like H, G and S·The solubility constant K,-K"] [NO]; however, since we assume that KNO3 is 100% dissociated in water and since [K7 . [NO], then if we let [K+)-[NO -x, K,,-x, Knowing the temperature at the solubility equilibrium point and having calculated Kp, you can calculate AG You can then take your data and plot InK (y-axis) vs. I/T ("K) to get a straight line. The slope of the line should be--dHR. You may assume that H is a constant over the limited temperature range you observed in the laboratory. Now that you know AG and AH, you can determine AS Eye protection required in today's exercise. Use care with hot surfaces. Avoid contacting potassium nitrate with skin, eyes, etc. Procedure 1. Using a buret filled with distilled water, mark volumes on one of two identical 8" test tubes beginning at the 15-ml point at 2-ml increments up to 50 milliliters. This will be used to determine the volumes in the other test tube. Use tape on the test tube to mark the increments 2 Add-20 grams of petacsium nitate to the other test nube and record the mass on the dat. sheet 3edd 15 ml of disued v..ser :., the test tube uing the bures and neaia a boiEnS water bath hed

Explanation / Answer

delta G = -R*T*ln K

Here value of R = 8.314

T can be taken as 298 K

for each value of K, you can calculate the value of delta G using above formula

K is Ksp which can be found by:

Ksp = [K+] [NO3-]

Let me help you with the 1st one

When [K+] = [NO3-] = 7.92

Ksp = [K+] [NO3-] = 7.92*7.92 = 62.7264

delta G = -R*T*ln K

             = -8.314*298*ln 62.7264

             = - 10254 J

            = - 10.254 KJ

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