Question

A certain liquid has a vapor pressure of 92.0 Torr at 23.0 °C and 210.0 Torr at 45.0 °C.

a. Calculate the value of Δ?∘vap for this liquid.

b. Calculate the normal boiling point of this liquid

Answer 1

a)

T1 = 23 oC

=(23 + 273)K

= 296 K

T2 = 45 oC

=(45 + 273)K

= 318 K

P1 = 92 torr

P2 = 2.1*10^2 torr

use:

ln(P2/P1) = (ΔH/R)*(1/T1 - 1/T2)

ln(2.1*10^2/92) = ( ΔH/8.314)*(1/296.0 - 1/318.0)

0.8253 = (ΔH/8.314)*(2.337*10^-4)

ΔH = 29358 J/mol

ΔH = 29.358 KJ/mol

Answer: 29.4 KJmol

b)

T1 = 23 oC

=(23 + 273)K

= 296 K

P1 = 92 torr

P2 = 7.6*10^2 torr (At normal boiling point, pressure is 760 torr)

ΔH = 29.358 KJ/mol

= 29358 J/mol

use:

ln(P2/P1) = (ΔH/R)*(1/T1 - 1/T2)

ln(7.6*10^2/92) = (29358.0/8.314)*(1/296.0 - 1/T2)

2.1115 = 3531.1523*(1/296.0 - 1/T2)

T2 = 360 K

= (360-273) oC

= 87 oC

Answer: 87 oC