Thermodynamics Sample Problems

1. Sketch a plot of the molar entropy of O2 from 0 K to 150 K. The normal melting and boiling points of O2 are 55 K and 90 K, respectively. Your graph should show qualitatively how the molar entropy of O2 varies with temperature.
Answer

2. Use tabulated data to estimate the temperature at which the vapour pressure of benzene is 10 Torr.
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3. Given the following data for ethanol.

Substance

standard molar enthalpy of formation, kJ.mol–1

standard molar free energy of formation, kJ.mol–1

standard molar entropy, J.K–1.mol–1

C2H5OH(l)

 –277.6  –174.8  161

C2H5OH(g)

 –235.4  –168.6  282

(a) Calculate the normal boiling point of ethanol.
(b) Calculate the vapour pressure of ethanol at 298 K.
(c) Calculate the free energy for the reaction below at 298 K.
C2H5OH(l) ---> C2H5OH(g, 200 Torr)
Answer