Use the following data to determine the normal boiling point, in K, of mercury.

Question

Use the following data to determine the normal boiling point, in K, of mercury. What assumptions must you make in order to do the calculation? H_g(l) DeltaH^infinity_f = 0(by definition) S^0 = 77.4 J/K.mol H_g(g) DeltaH^infinity_f = 60.78 kJ/mol S^0 = 174.7 J/K.mol the standard enthalpy of formation and the standard entropy of gaseous benzene are 82.9 kJ/mol and 269.2 J/K mol, respectively. The standard enthalpy of formation and the standard entropy of liquid benzene are 49.04 kJ/mol and 172 8 J/K mol, respectively. Calculate DeltaHdegree, DeltaSdegree, and DeltaGdegree for the process at 25degree C. C_6 H_6(l) rightarrow C_6 H_6 (g) DeltaHdegree =______________kJ/mol DeltaSdegree =______________J/K.mol DeltaGdegree =______________kJ/mol Is the reaction spontaneous at 25.00degree C?

Explanation / Answer

9-

Write the Gibbs free energy variation as a function of H, S and T:

G° = H° – T*S°

The Hg(l) /Hg(g) equilibrium is

Hg(l) <----> Hg(g)

Let P = Hg vapour pressure

G° = H° – T*S° = -RTlnP

At boiling point P = 1 atm. Then:

G° = H° – T*S° = 0

H° = T*S°

T = boiling point = H°/ S°

H° = H°f(Hg(g)) - H°f(Hg(l)) = 60.78 kJ/mol

S° = 174.7 - 77.4 = 97.3 J/K mol

T = 60780/97.3 = 625 K = 351 °C

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