Question

Calculate the entropy, enthalpy and free energy of dilution when the 10 mL of 50mM pH 7.2 potassium phosphate is diluted to 100 mL at room temperature.

Answer 1

DG_dilution= RT ln (C2/C1)                             where C1>C2

DS_dilution= R ln (C1/C2)

According to the given data

DG_dilution= RT ln (C2/C1) = 8.314 J mol^-1 K^-1 * 298 K * ln (1/10) = -5704.82 J mol^-1

DS_dilution= R ln (C1/C2) = 8.314 J mol^-1 K^-1 * ln (10/1)= 19.14 J mol^-1 K^-1

As we know DG= DH-T*DS

DH_dilution=DG_dilution+T*DS_dilution =  -5704.82 + 298*19.14= 0