Chemical Engineering Thermodynamics II

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Chemical Engineering Thermodynamics II

• Dr. Perla B. Balbuena JEB 240
• balbuena_at_tamu.edu
• Website http//research.che.tamu.edu/groups/Balbu
  ena/Courses/CHEN20354-Thermo20II-20Spring2015/
  CHEN20354-Thermo20II-Spring2015.htm
• (use VPN from home)
• ?CHEN 354-Fall 14

TA Julius Woojoo Choi, drspchoi_at_gmail.com
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TAs office hours

• Julius Woojoo Choi, drspchoi_at_gmail.com
• Office hours Thursdays, 4-5pm, Office 613

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TEAMS

• Please group in teams of 4-5 students each
• Designate a team coordinator
• Team coordinator Please send an
• e-mail to balbuena_at_tamu.edu stating the names
  of all the students in your team (including
  yourself) no later than next Monday
• First HW is due January 28.

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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 gt work (energy
  transfer)
• Temperature differences gt heat transfer
• Differences in chemical potential gt 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
f
e
d
c
b
a

• What happens from (a) to (f) as volume is
  compressed at constant T.

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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) dT
• Pure liquid in equilibrium with its vapor, if a
  differential amount of liquid evaporates at
  constant T and P, then
• d(nG) 0
• n constant gt ndG 0 gt dG 0
• Gl Gv
• Equality 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

mi 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
• mia mib (for i 1, 2, 3,.n)
• Ta Tb
• Pa Pb

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A liquid at temperature T
A liquid at temperature T in a closed container

• The more energetic particles escape

Vapor pressure
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Fugacity of 1 f1
Fugacity of 2 f2
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For a pure component

• ma mb

For a pure component, fugacity is a function of T
and P
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For a mixture of n components

• mia mib for all i 1, 2, 3, n
• in a mixture

Fugacity is a function of composition, T and P
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Lets recall Raoults law for a binary
We need models for the fugacity in the vapor
phase and in the liquid phase
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Raoults law
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Raoults law

• Model the vapor phase as a mixture of ideal
  gases
• Model the liquid phase as an ideal solution

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VLE according to Raoults law
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Homework 1download from web siteDue
Wednesday, 1/28