The table lists the thermodynamic parameters for three chemical reactions, viz..

Question

The table lists the thermodynamic parameters for three chemical reactions, viz.. hydration of ions, dissociation of acetic acid in water, and transfer of the nonpolar hydrocarbon toluene to water.

b. Which of these reactions is spontaneous? Is it driven by enthalpy, entropy, or by both enthalpy and entropy? Explain.

c. Calculate the Keq, i.e. Ka, for dissociation of acetic acid under these conditions?

d. Based on the Keq calculated in (c), calculate Keq? for dissociation of acetic acid. How many fold greater is Keq? than Keq? What is the practical consequence of this difference for the cell?

All steps to the solutions of the problems must be shown. Round your answers as appropriate, but no more than three significant figures.

TABLE 3.2 Thermodynamic Parameters for Several Simple Processes AH kJ/mol Process Hydration of ionst 760.0 Na+ (g) Cl (g) Na+ (aq) Cl (aq) Dissociation of ions in solution 10.3 H2O CH3COOH H30 CH3COO Transfer of hydrocarbon to water 1.72 Toluene (in pure toluene) toluene (aqueous *All data collected for 25°C. tBerry, R. S., Rice, S. A, and Ross, J. 1980. Physical Chemistry. New York: John Wiley. Tanford, C, 1980. The Hydrophobic Effect. New York: John Wiley. AS kJ/mol K 0.185 -0.126 0.071 AG kJ/mol 705.0 27.26 22.7 40 kJ/mol K 0.143 0.265

Explanation / Answer

deltaH= deltaH- TdeltaS, T= 298K

for the 1st reaction, deltaGo = deltaH- TdeltaS = -760+298*0.185= -705 Kj/mole. The process is spontaneous since deltaG is –ve.

Fpr the 2nd reaction, deltaGo = -10.3+298*0.126 =27.24 Kj/mol. This is not spontaneous

For the 3rd reaction, deltaGo = 1.72+0.071*298= 22.8777 Kj/mol. Not spontaneous.

The reactions are driven by both enthalpy and entropy

-deltaGO= -RT lnK

lnK= -deltaG0/RT = -22.877/(298*8.314) , K= 0.999

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