GATE Chemical Engineering Practice Quiz

Question 1

For a pure component at low pressure, which statement about fugacity in the vapor phase is most accurate?

Accepted Answer

Fugacity approaches pressure as pressure tends to zero.

Question 2

At vapor-liquid equilibrium for a pure substance, which equality must hold?

Accepted Answer

Fugacity in liquid equals fugacity in vapor.

Question 3

In a gamma-phi formulation for VLE, the equilibrium condition for component i including the Poynting correction is

Accepted Answer

$y_i \phi_i P = x_i \gamma_i f_i^{sat} \exp\left[\dfrac{v_i^L(P-P_i^{sat})}{RT}\right]$

Question 4

For a binary mixture at fixed T and P, suppose component 1 obeys $y_1 \phi_1 P = x_1 \gamma_1 P_1^{sat}$ and all quantities except $\gamma_1$ are unchanged. If $\gamma_1$ increases, what happens to the equilibrium vapor composition $y_1$?

Accepted Answer

$y_1$ increases because larger $\gamma_1$ raises liquid escaping tendency.

Question 5

In the modified Raoult's law for low-pressure VLE of a non-ideal liquid and nearly ideal vapor, the equilibrium relation for component i is best written as

Accepted Answer

$y_i P = x_i \gamma_i P_i^{sat}$