Instructional Media as Teaching Aids Maria Estela Teo-Balbuena.
Chemical Engineering Thermodynamics II Dr. Perla B. Balbuena: JEB 240 Web site: 20.
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Transcript of Chemical Engineering Thermodynamics II Dr. Perla B. Balbuena: JEB 240 Web site: 20.
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Chemical Engineering Thermodynamics II
• Dr. Perla B. Balbuena: JEB 240 [email protected]• Web site:
https://secure.che.tamu.edu/classes/balbuena/CHEN%20354-Thermo%20II-Spring%2012/CHEN%20354-Thermo%20II-Spring%2012.htmor:
• http://research.che.tamu.edu/groups/balbuena/courses.htm
(use VPN from home)CHEN 354-Spring 12
TA: Mian Huang; e-mail:[email protected]
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TA office hours • Thursdays 1:30 to 2:30 pm; Rm 501
• Or by appointment, please e-mail to Mian Huang:[email protected]
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TEAMS • Please group in teams of 4-5 students
each• Designate a team coordinator • Team coordinator: Please send me an
e-mail stating the names of all the students in your team (including yourself) no later than next Monday
• First HW is due January 26th
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Introduction to phase equilibrium
Chapter 10 (but also revision from Chapter 6)
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Equilibrium• Absence of change• Absence of a driving force for change• Example of driving forces
– Imbalance of mechanical forces => work (energy transfer)
– Temperature differences => heat transfer
– Differences in chemical potential => mass transfer
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Energies• Internal energy, U
• Enthalpy H = U + PV
• Gibbs free energy G = H – TS
• Helmholtz free energy A = U - TS
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Phase Diagram Pure Component
a
d
c
b
e
What happens from (a) to (f) as volume is compressed at constant T.
f
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P-T for pure component
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P-V diagrams pure component
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Equilibrium condition for coexistence of two phases
(pure component)• Review Section 6.4
• At a phase transition, molar or specific values of extensive thermodynamic properties change abruptly.
• The exception is the molar Gibbs free energy, G, that for a pure species does not change at a phase transition
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Equilibrium condition for coexistence of two phases
(pure component, closed system)
d(nG) = (nV) dP –(nS) dTPure liquid in equilibrium with its vapor, if a differential amount of
liquid evaporates at constant T and P, then
d(nG) = 0n = constant => ndG =0 => dG =0
Gl = GvEquality of the molar or specific Gibbs free energies (chemical
potentials) of each phase
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Chemical potential in a mixture:
• Single-phase, open system:
i
inTPinPnT
dnnnGdT
TnGdP
PnGnGd
j,,,,
)()()()(
i :Chemical potential of component i in the mixture
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Phase equilibrium: 2-phases and n components
• Two phases, a and b and n components:
Equilibrium conditions:
ia = i
b (for i = 1, 2, 3,….n)
Ta = Tb
Pa = Pb
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A liquid at temperature T
The more energetic particles escape
A liquid at temperature T in a closed container
Vapor pressure
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Fugacity of 1 = f1 Fugacity of 2 = f2
222̂ fxf id
111̂ fxf id
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For a pure component =
iiii fRTTG ln)(
For a pure component, fugacity is a function of T and P
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For a mixture of n components
i = i
for all i =1, 2, 3, …n
in a mixture:
iii fRTT ˆln)(
Fugacity is a function of composition,T and P
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Lets recall Raoult’s law for a binary
lv
lv
ff
ff
22
11
ˆˆ
ˆˆ
We need models for the fugacity in the vapor phase and in the liquid phase
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Raoult’s law
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Raoult’s law• Model the vapor
phase as a mixture of ideal gases:
• Model the liquid phase as an ideal solution
ivi Pyf ˆ
isati
li xPf ˆ
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VLE according to Raoult’s law:
222
111
xPPy
xPPysat
sat
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Homework # 1
download from web site
Due Wednesday, January 25th, at the beginning of the class