The chart below was obtained in the study of the solubility of a salt. Use the i

Question

The chart below was obtained in the study of the solubility of a salt. Use the information on the chart to determine the Delta G degree for this reaction at 298K. How does the solubility of this salt change when the temperature increases? a. Delta G degree = 56 kJ/mol; the solubility of this salt increases when temperature goes up b. Delta G degree = -9.1 kJ/mol; the solubility of this salt decreases when temperature goes up c. Delta G degree = -7. 9 kJ/mol; the solubility of this salt decreases when temperature goes up d. Delta G degree = 9.1 kJ/mol; the solubility of this salt increases when temperature goes up e. Delta G degree = 56 kJ/mol; the solubility of this salt decreases when temperature goes up (3.57 pts for the correct value of Delta G degree, but the wrong solubility reasoning)

Explanation / Answer

Ans. #1. In the graph, Y-axis indicates lnK and X-axis depicts (1/T).

T 298 K, putting X = 1/T = 1/ 298 in he trendline equation-

            -ln K = - 7901.9 x (1/ 298) + 4.1253

            or, -ln K = - 26.5164 + 4.1253

            Or, -ln K = - 22.3911

            Hence, ln K = 22.3911

#2. Now, using: dG0 = - RT lnK     - equation 1

            Where,

                        dG0 = Standard Gibb's free energy

                        R = Universal gas constant = 0.008314 kJ mol-1 K-1

T = Temperature in kelvin

K = Equilibrium constant

Putting the values in equation 1-

            dG0 = - (0.008314 kJ mol-1 K-1) x 298 K ln ( 22.3911)

            or, dG0 = - 7.70 kJ/mol

#C. For a reaction-

            AB(s) ----------> A+(aq) + B-(aq)

Equilibrium constant, K = [A+] [B-]

See the graph-

            Increase in temperature (towards the left on Y-axis) increase the value of -lnK (from more negative towards zero).

So, “increase in temperature decrease the value of + lnK “

Therefore, decrease in value of lnK (directly proportional to lnK) with increase in temperature result – decrease in solubility because a lower K means lower concentrations of [A+] and [B-].

Therefore, correct option = C (closet value of dG0 ; explanation is correct.).

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