Question

a. The standard enthalpy of vaporization of an inorganic compound is 38.9 kJ/mol. If the temperature at which this phase change occurs is 221.72 °C, determine ΔS°_vap (in J/mol/K) for this compound. Report your answer to three significant figures.

b. The entropy of freezing of an organic compound is -21.0 J/mol/K. If ΔH°_freez is -14.01 kJ/mol, determine the temperature (in K) at which this phase change occurs. Report your answer to two decimal places

Answer 1

(a). Standard enthalpy of vaporization, H^o_vap = 38.9 kJ/mol

= 38900 J/mol

Temperature = 221.72 oC = 494.87 K

S^o_vap = H^o_vap / T

= 38900 / 494.87

S^o_vap = 78.6 J/mol.K

(b). S^o_fus = - 21.0 J/mol.K

H^o_fus = -14.01 kJ/mol = - 14010 J/mol

S^o_fus = H^o_fus / T

T = - 14010 / - 21

= 667.14 K

Temperature =  667.14 K