Project ForgeChemical Reaction Engineering
Ideal Reactor Design
GATE 2017
Hard
A+B→R+S (gas phase, constant-volume isothermal batch), all non-condensable except R (Psat,R=40kPa). Equimolar A,B at total P=100kPa, CA0=CB0=12.5 mol/m³, (−rA)=0.08CACB. The time at which R just starts condensing, rounded to 1 decimal place, is
4 s(± 0.15 accepted)
Explanation
With CA0=CB0, C(t)=12.5/(1+t) (since 0.08×12.5=1). CR=12.5−C. Conversion factor: 100kPa/25mol/m³=4kPa per mol/m³. Setting P_R=CR×4=40 ⟹ CR=10 ⟹ C=2.5. From C=12.5/(1+t): t=(12.5/2.5)−1=4.0s.
Source: GATE CH 2017 (2017)
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