Question

The pressure of a compound at 200 K is 10 mm Hg and at 400 K it is 50 mm Hg, what is the pressure at T = 250 K?

(a) 18.1 mm Hg

(b) 24.2 mm Hg

(c) 36.3 mm Hg

(d) 48.4 mm Hg

The question was posed to me in unit test.

I'm obligated to ask this question of Modeling and Predicting Vapor Pressure in section Real Gases: Equations of State, Single Component Two Phase Systems, Saturation & Condensation of Basic Chemical Engineering

Answer 1

Right choice is (a) 18.1 mm Hg

To elaborate: Let the pressure of the compound is given by ln p* = a + b/T, => ln 10 = a + b/200, ln 50 = a + b/400, => ln 5 = -b/400, => b = -643.7, => a = 5.5, => At T = 250 K, ln p* = 5.5 – 643.7/250 = 2.9, p = 18.1 mm Hg.