Chemical Engineering Thermodynamics Ch. 20 Exam || Questions & Answers 2025 (100% Correct)

Chemical Engineering Thermodynamics
Ch. 20 Exam || Questions & Answers
2025 (100% Correct)
Fugacity - ANSWER - The "Tendency to escape". It is the real gas equivalent of a
partial pressure.
Initally defined as muei-muei reference=RTln(f liq hat/f liq hat ref)

The reference state for chemical potental or fugacity is taken at the same what as the
system - ANSWER - Temperature of the system

Fugacity coefficient of a solution equation - ANSWER - Phi hat i= f hat i/ pi,sys
OR
Phi hat i= f hat i/(yi*Psys)
Or, for pure species
Phi i= f i/(Psys)

Meaning of fugacity coefficients - ANSWER - Coefficient equal to one means ideal
Coefficient less than one so the attractive forces dominate
Coefficient greater than one so the repulsive forces dominate because it wants to
escape

What are the revised criteria for equilibrium? - ANSWER - Ta=Tb
Pa=Pb
f hat a=f had b

For fugacity calculation of a pure gas, what are the equations used and the reference
state parameters - ANSWER - gi-gi ref=RTln(fi vap/Plow)
Phi,i vap=f,i vap/Psys
Phi,i is also found with the tables, EOS, or General corrections
Pref=Plow
Tref=Tsys

To obtain fugacity, thermodynamic data can be collected from three sources, what are
they and how can we get the data? - ANSWER - 1. Tables
Just find a table with h, s, T, and P and using the system T and P, calculate G.
2. EOS
With our equation for ideal fugacity of a pure gas, substitute in for g,i-g,i ref the integral
of Plow to P of v,mdP.
3. Generalized Correlations
ln(Phi)=ln(Phi)^0+omega*ln(Phi)^1
The equation to use here is

, ln(Phi),i vap=the integral from Pideal to P of (z,i-1)dP/P. Equation interms of reduced
pressure has the same terms

Fugacity equation and reference state parameters for an ideal gas mixture - ANSWER -
f hat reference=p,i reference= yi,sys*Plow, where Pref=Plow, Tref=Tsys, n,i ref=n,isys

Using equations of state:
RTln(f,i hat vap/yi*plow)= -integral from (ntotal*RT/Plow) to V of (dP/dn,i)dV

Lewis Fugacity Rule - ANSWER - It states that we can, potentially, estimate a vapor's
solution fugacity coefficent with its pure species FC. It uses the ASSUMPTION, that
interactions are nearly identical in a mixture, which simplifies calculations. So, we may
use f,i hat vap=yi*phi,i vap*P
OR
f,i hat vap=y,i*f,i vap

What are the three things that must be satisfied for a vapor fugacity to be calculated
with lewis fugacity rule? - ANSWER - 1. P is low or T is high to correspond with an ideal
gas
2. Component a is present in large excess (yb is small)
3. The chemical nautre of species a is similar to that of all the other components

For ideal gases, what are the property changes of mixing? - ANSWER - delta
v,mix,ideal=0
delta h,mix,ideal=0
delta s,mix,ideal= -Rsigma(yi*ln(yi))
delta g,mix,ideal=RTSigma(yi*ln(yi))

For ideal solutions, what are the property changes of mixing? - ANSWER - delta
v,mix,ideal=0
delta h,mix,ideal=0
delta s,mix,ideal= -Rsigma(xi*ln(xi))
delta g,mix,ideal=RTSigma(xi*ln(xi))

Lewis/Randall rule - ANSWER - It calculates a pure species fugacity of a liquid species.
f,a ideal= f,a ref= f,a for a-a interactions

What is the difference between Lewis/Randall and Henry's law - ANSWER - L/R the
reference state is called a solvent and in henry's its called a solute. Henry's and L/R's
are the constraits of real fugacity behavior.

Activity coefficent - ANSWER - Tells us how active the liquid is related to our choice of
reference state; Tells us how far the deviation from ideal is.
Gamma,i=f,i hat liq/f,i hat ideal=f,i hat liq/(xi*f,i ref)

In liquids, what is the difference to deciding a reference state? - ANSWER - Pref=Psys