Question

For toluene determine:
a) Vapor pressure at 100 ° C.
b) Its boiling temperature at a pressure of 530 torr.
c) Draw the liquid-vapor equilibrium curve from 13 to 136 ° C.

Answer 1

a) Vapor pressure at 100 ° C

Using Clausius clapeyron equation:

ln(P1/P2) = (ΔH_vap/R)((1/T2) - (1/T1)).

• ΔH_vap: The enthalpy of vaporization of the liquid.
• R: The real gas constant, or 8.314 J/(K × Mol).
• T1: The temperature at which the vapour pressure is known (or the starting temperature.)
• T2: The temperature at which the vapour pressure is to be found (or the final temperature.)
• P1 and P2: The vapour pressures at the temperatures T1 and T2, respectively.

Assumptions:

1. Consider initial temperature T₁ = 25^oC = 273+25 = 298K, T₂ = 100 +273 = 373K
2. Consider initial pressure P₁ = 101325 Pa, P₂ =?
3. Taking the value of ΔH_vap = 33.18 kJ/ mol

Substituting the values in the equation

ln(101325/P₂) = (33180/8.314)(1/373 - 1/298)

P₂ = 1496570 Pa

b) Its boiling temperature at a pressure of 530 torr.

1 torr = 133.322 Pa

530 torr = 70661 Pa

Assumptions:

1. Consider initial temperature T₁ = 25^oC = 273+25 = 298K, T₂ = ?
2. Consider initial pressure P₁ = 101325 Pa, P₂ = 70661 Pa
3. Taking the value of ΔH_vap = 33.18 kJ/ mol

Substituting the values in the Clausius clapeyron equation

ln(101325/70661) = (33180/8.314)(1/T₂ - 1/298)

T₂ = 290.655K = 17.65^oC