Pre-Laboratory Exercise Thermodynamices of Dissolving Potassium Nitrate Consider

Question

Pre-Laboratory Exercise Thermodynamices of Dissolving Potassium Nitrate Consider the process of dissolving KCl(s) in water KCI (s)-K' (aq) + Ci (aa) From a procedure identical to the one in this experiment, the data on the third page of the spreadsheet were obtained. Carefully go over the spreadsheet and be sure you understand how each calculation in the table was made (you can hover over the cell to see what calculation was performed or use Excel's reveal formulas function). To reveal the formulas, press CTRL+ (grave accent) after highlighting the cells you want to view. 1. What is the slope of the line obtained in the plot? 2. Calculate the value of AH for dissolving KCI in water. 3. Calculate AS for the reaction at 20.0°c

Explanation / Answer

KSp is releated to gibbs free energy change (deltaG) as

deltaG =-RT lnKSp, deltaG= deltaH-T*deltaS

hence lnKSP= -deltaH/RT+ deltaS/R

so the plot of lnKSp vs 1/T gives a slope of -deltaH/R and intercept of deltaS/R, R is gas constant= 8.314 J/mole.K

from the plot of equation of best fit, the slope = -1445= -deltaH/R, deltaH= 1445*8.314 J/mol.e=12014 J/mole= 12.014 Kj/mole, the intercept is deltaS/R= 7.5269, deltaS= 62.6 J/K.

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