Question

Chloroform, CHCl₃, a volatile liquid, was once used as an anesthetic but has been replaced by safer compounds. Chloroform has a normal boiling point at 61.7 °C (1atm) and has a heat of vaporization of 31.4 kJ/mol. What is its vapor pressure at 25.0 °C.

Answer 1

Clausius- Clapeyron equation can be written as

In (P2/P1) = ΔH/R (1/T1 - 1/T2) ---Eq(1)

Given that P1 = 1 atm

P2 = ?

ΔH = heat of vaporization = 31.4 kJ/mol = 31400 J/mol

Initial temperature T1 = 61.7 °C = 61.7 + 273 K = 334.7 K

Final temperature T2 = 25oC = 25 + 273 K = 298 K

R= universal gas constant = 8.314 J/K/mol

substitute all these velues in eq (1),

In (P2/P1) = ΔH/R (1/T1 - 1/T2) ---Eq(1)

In (P2/1) = (31400 / (8.314) [(1/334.7 - 1/298)]

P2 = 0.25 atm

Therefore, vapor pressure of Chloroform at 25.0 °C =  0.25 atm