Chloroform, formerly used as an anesthetic and now believed...

Chloroform, formerly used as an anesthetic and now believed to be a carcinogen, has a heat of vaporization $\Delta H_{\text {vaporianion }}=31.4 \mathrm{~kJ} \mathrm{~mol}^{-1}$. The change, $\mathrm{CHCl}_{3}(l)$ $\mathrm{CHCl}_{3}(g)$, has $\Delta S^{\circ}=94.2 \mathrm{~J} \mathrm{~mol}^{-1} \mathrm{~K}^{-1}$. At what tempera- ture do we expect $\mathrm{CHCl}_{3}$ to boil (i.e., at what temperature will liquid and vapor be in equilibrium at 1 atm pressure)?

Chloroform, formerly used as an anesthetic and now believed to be a carcinogen, has a heat of vaporization $\Delta H_{\text {vaporianion }}=31.4 \mathrm{~kJ} \mathrm{~mol}^{-1}$. The change, $\mathrm{CHCl}_{3}(l)$
$\mathrm{CHCl}_{3}(g)$, has $\Delta S^{\circ}=94.2 \mathrm{~J} \mathrm{~mol}^{-1} \mathrm{~K}^{-1}$. At what tempera-
ture do we expect $\mathrm{CHCl}_{3}$ to boil (i.e., at what temperature will liquid and vapor be in equilibrium at 1 atm pressure)?

Key Concepts

Boiling Point and Phase Equilibrium

This concept refers to the temperature at which a liquid converts to a gas (and vice versa) such that the rates of evaporation and condensation are equal, establishing a dynamic equilibrium under a given pressure. It is fundamental in understanding phase transitions and the conditions under which substances change state.

Enthalpy of Vaporization

Enthalpy of vaporization is the amount of energy required to convert one mole of a liquid into its vapor at constant pressure. It reflects the strength of intermolecular forces in the liquid and is a crucial parameter in determining the energy balance during the phase change from liquid to gas.

Entropy Change in Phase Transitions

Entropy change during a phase transition measures the increase in disorder as a substance transitions from a more ordered liquid phase to a more disordered gaseous phase. This increase in entropy is a driving force in the vaporization process and plays a key role in determining the conditions for equilibrium.

Gibbs Free Energy and the Equilibrium Condition

Gibbs free energy combines enthalpy and entropy changes to determine the spontaneity of a process at constant temperature and pressure. At the boiling point, the condition of equilibrium is achieved when the Gibbs free energy change is zero (?G = 0), linking the concepts of enthalpy and entropy changes.

Determination of Equilibrium Temperature using ?H/?S

This concept involves calculating the temperature at which a phase change occurs by setting the Gibbs free energy change to zero, leading to the relationship T = ?H/?S. It provides a simplified method to estimate the equilibrium (boiling) temperature based on the energetic and entropic characteristics of the phase transition.

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