# Distillation Design Questions and Answers – Vapour Liquid Equilibrium

This set of Distillation Design Multiple Choice Questions & Answers (MCQs) focuses on “Vapour Liquid Equilibrium”.

1. Which of the following shows the correct Gibbs phase rule equation?
a) F=C-P+2
b) P=C+P
c) C=F-P+2
d) C=P-F

Explanation: According to Gibb’s F=C-P+2 for any system, where F is degree of freedom, C is number of components and P is the number of phases.

2. The higher the concentration of volatile species, the distillation
a) The higher the rate of liquid flow
b) The lower the rate of Separation
c) The higher the rate of separation
d) Cannot be specified

Explanation: Volatility is directly proportional to the ease of separation (α) while it is inversely proportional to difficulty of separation.

3. VLE data once obtained is represented on which scale?
a) Binary Scale (0<x<1)
b) Pressure Scales (0<Pa<1)
c) Temperature Ranges (T1<x<T2)
d) Not specific

Explanation: Binary scales are most suitable as they represent mole fractions of the both species x* and y* at all conditions.

4. When the boiling temperature is plotted against the liquid composition, then it is called
a) Cooling Curve
b) Heating Curve
c) Bubble point curve
d) Volatility Phase Diagram

Explanation: The (T-x) curve is called as Bubble point Curve, Where T is boiling temperature and x is the mole fraction of the liquid.

5. When the temperature is plotted against the equilibrium vapor, then it is called
a) Condensing Curve
b) Dew Point curve
c) Equilibrium Curve
d) Bubble Curve

Explanation: The (T-y*) curve is called as Dew point Curve, Where T is boiling temperature, and y is the equilibrium moles of the gaseous components.

6. The K value can be expressed as
a) y/x
b) yi/x
c) x/y
d) yi/xi

Explanation: The ratio of mole fraction of components in vapor and liquid phase is called as K value.

7. The Relative Volatility of components i and j can be defined as
a) Ki/Kj
b) K/Kj
c) yi/y
d) xi/x

Explanation: The ratio of K values is defined as the relative volatility, Where Ki is the gaseous components and Kj is the fluid components.

8. Given that αAB=2.0, Then equilibrium ratio of B is KB=0.7, Estimate αBA ?
a) 0.9
b) 0.65
c) 0.5
d) 0.6

Explanation: As α=KB/KA, 2.0= 0.7/KA, KA = 0.35 and αAB =KA/KB =0.35/0.7 = 0.5.

9. Which system can be said as an Ideal system that obeys?
a) Henrys Law
b) Daltons Law
c) Phase Rule
d) Cremer’s rule

Explanation: The system that obeys Henry’s and Dalton’s Law is called an ideal system, as they are derived from the ideal gas relation PV=Nrt.

10. Which of the below is the Dalton’s Law?
a) pi = yi/P
b) x = yi/ pi
c) pi = yi/x
d) pi = xi/y

Explanation: According to Dalton’s law the partial pressure of component is solution is equal to product of its mole fraction and vapor pressure of pure components.

Sanfoundry Global Education & Learning Series – Distillation Design.
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