Question

A certain liquid has a vapor pressure of 92.0 Torr at 23.0 ∘C and 344.0 Torr at 45.0 ∘C. Calculate the value of Δ?∘vap for this liquid. Δ?∘vap= kJ/mol Calculate the normal boiling point of this liquid. boiling point: ∘C

Answer 1

The equation which relates pressure and temperature for the equilibrium between two phases is 'Clausius-Clayperon' equation, which is:

P1 and P2 are vapor pressures at T1 and T2, respectively

is the molar heat of vaporisation,

R is the Universal gas constant (8.314 J/K.mol)

We know that,

T (in Kelvin) = 273 + T(in )

i) 23.0

T(in K) = 273 +23 = 296 K

ii) 45.0

T(in K) = 273 +45 = 318 K

Given the data:

S.No	Pressure (Torr)	Temperature (in K)
1	92.0	296
2	344.0	318
3	760.0	? (Normal Boiling Point)

a)  :

Using data from 1 and 2, and put in clausius-clayperon equation:

(1 J = 1/1000 kJ)

b) Normal boiling point:

Using data from 1 and 3, and put in clausius-clayperon equation:

Hence, Normal Boiling point = 60.0