Subtopic: Water activity, sorption and desorption isotherms
Question Statement:
Slope and intercept of the BET equation relating a_w/[x(1−a_w)] and a_w are 18 and 2, respectively. The values of thermodynamic constant C and BET monolayer moisture content x_m (%) are respectively
Options:
(A) 40 and 20
(B) 30 and 15
(C) 20 and 10
(D) 10 and 5
Official Answer Key:
D
Step-by-Step Solution & Explanation
The linearized BET equation is a_w/[x(1−a_w)] = 1/(x_m·C) + [(C−1)/(x_m·C)]·a_w, so: intercept = 1/(x_m·C) = 2, and slope = (C−1)/(x_m·C) = 18.
Dividing slope by intercept: (C−1) = 18/2 = 9 ⇒ C = 10.
From the intercept: x_m = 1/(2×C) = 1/20 = 0.05 = 5%. Answer: (D) 10 and 5.
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