ChemE 260 Internal Energy, Enthalpy

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ChemE 260 Internal Energy, Enthalpy The NIST
Webbook

• Dr. William Baratuci
• Senior Lecturer
• Chemical Engineering Department
• University of Washington
• TCD 3 A BCB 2 9 11, Supplement

April 5, 2005
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Internal Energy Enthalpy

• Internal Energy
• Non-nuclear energy stored within molecules
• Sum of the vibrational, translational and
  rotational kinetic energies
• U strong fxn of T and a weak fxn of P
• U ? sharply as T ? but U ? slightly as P ?.
• Ideal Gas, Incompressible Liquids, Solids
• U fxn(T) only
• U ? fxn(P)
• Enthalpy
• H U P V dH dH d(PV) ?H ?U ?(PV)
• H strong fxn(T)
• H moderate fxn(P)
• Ideal Gas H ? fxn(P)S

Baratuci ChemE 260 April 5, 2005
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NIST Webbook
Baratuci ChemE 260 April 5, 2005
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Reference State

• We cannot determine an absolute U or H in the way
  we can determine an absolute T.
• We must choose a reference state andassign
  0 or 0 at that state.
• Calculate all other values of and
  relative to the reference state.
• You cannot use thermodynamic data from different
  sources that are based on different reference
  states without correcting for the difference in
  reference state !!

Baratuci ChemE 260 April 5, 2005
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Generating a Saturated Temperature Table
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Baratuci ChemE 260 April 5, 2005
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Saturated Liquid Properties
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Saturated Vapor Properties
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Extra Info from the NIST Webbook
Baratuci ChemE 260 April 5, 2005
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Example 1

• Determine the Tsat, and of saturated
  liquid ammonia at 300 kPa. (Default ref. state)
• Ans. Tsat -9.2243 oC U 300.25 kJ/kg H
  300.71 kJ/kg

Baratuci ChemE 260 April 5, 2005
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Example 2

• Determine the , and of butane at
  14.696 psia and 77oF in units of Btu, lbm and
  ft3. (Default ref. state)
• Ans. V 6.5394 ft3/lbm U 251.92Btu/lbm H
  269.71 Btu/lbm

Baratuci ChemE 260 April 5, 2005
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Example 3

• Determine the , and of a
  saturated mixture of R-123 at 40oC and x 0.30.
  (Default ref. state, kJ, mole, m3)
• Ans. Psat 3.5752 Kpa Usat liq 24.660
  kJ/mol , Usat vap 52.800 kJ/mol , Ux0.03
  33.102 kJ/mol Hsat liq 24.660 kJ/mol, Hsat vap
  54.731 kJ/mol, Hx0.03 33.681 kJ/mol Vsat
  liq 9.4405 x 10-5 m3/mol, Vsat vap 0.54014
  m3/mol , Vx0.03 0.16211 m3/mol

Baratuci ChemE 260 April 5, 2005
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Next Class

• Heat Capacities
• How much does the temperature of 1 mole or kg of
  a substance change when 1 J is added ?
• Phase Changes
• Latent heats of vaporization, fusion and
  sublimation
• Hypothetical Process Paths
• HPPs make it easier to calculate how much a
  property changes during any real process.

Baratuci ChemE 260 April 5, 2005