Thermo, set 3

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Thermo, set 3
2010-03-17 04:49:49
Engineering Thermodynamics

Chemical Thermodynamics
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  1. enthalpy
    • a convenient grouping of the internal energy, pressure, and volume
    • H = U + PV or h = u + pv [kJ/kg]
    • Heat flow for process at constant pressure
    • Q = change in enthalpy
  2. saturation pressure
    pressure at which the liquid and vapor phases are in equilibrium at given temp
  3. saturation temperature
    the temperature at which the liquid and vapor phases are in equilibrium at given pressure
  4. enthalpy of vaporization
    (latent heat of vaporization), h_fg - the amount of energy needed to vaporize a unit of mass of saturated liquid at a given temp /pressure
  5. moisture
    1 - x, where x is quality x, or mg/mg+mf
  6. Lever Rule
    • x = (y-yf)/yfg
    • where y may be replaced with v, u, h, or s, and x is the mass of saturated vapor divided by total mass
  7. superheated
    given tempreature is greater than the saturation temp for given pressure
  8. compresed liquid
    when the pressure is greater than the saturation presure at a given temp
  9. How to choose the right table
    Compare the known state properties to the properties in the saturation region
  10. compressed liquid region
    v < vf
  11. saturation region
    vf < v < vg
  12. superheated region
    vg < v
  13. equations of state
    relationship between the state variables, temperature, pressure, and specific volume
  14. ideal gas law
    • Pv = RT
    • Used when 1) pressure is small compared to critical pressure, 2) Temp is twice critical temp and pressure is less than 10 times critical pressure
  15. Gas constant R
    • R = Ru/M
    • Ru is universal gas constant
  16. mass
    m = NM, the number of moles times the molar mass
  17. Combined gas law
    • Ideal gas for a fixed mass - m1 = m2, or
    • PV/RT (1) = PV/RT (2)
  18. 1st Law of Thermo
    • Expression of the conservation of energy, energy can cross boundary of closed system as work or heat
    • dU = d q - pdV
    • If energy transfer is due to temp. diff, it's heat, otherwise it's work.
  19. State function
    of energy - value depends on final and initial states, not on internal energy used
  20. Chemical potential
    proportionality constant m; change in internal energy is proportional to the number of particles dn added to the styem
  21. Combined 1st and 2nd laws
    dU = TdS – PdV + mdn
  22. Kelvin Statement
    It is not possible for the absorption of heat from a reservoir to complete convert to work
  23. Entropy
    • measure of dispersal of energy (molecular disorder)
    • Non-conserved property; as entropy increases, it increases entropy of universe
    • Increases as DOF increases
  24. Isentropic
    • Entropy does not change (either by heat transfer or irreversibilities)
    • Or, reversible adiabatic process
  25. Reversible Process
    ability to run a process back and forth infinitely without losses (i.e. perfect pendulum, mass on string, etc.)
  26. Irreversible Process
    • i.e. dropping clay, hammering a nail, breaking glass
    • Sources; friction, pressure, voltage, temp, and concentration drops
  27. adiabatic
    • no heat is gained or lost in a system
    • q=0
  28. Engineering devices
    work best when isentropic and irreversibilities are eliminated
  29. Disorder
    naturally increases, and natural processor proceed spontaneously to order
  30. 2nd Law of Thermo
    • entropy of isolated system, i.e universe, increases in any spontaneous change
    • deltaStot>0
    • Entropy of universe continuously changing
    • irreversible process of transferring heat from hot to cold body
  31. spontaneous
    • process that occurs without ongoing outside intervention
    • i.e. ice melting at room temperature, expansion of gas in space
  32. Molecular motion
    • Translational - entire molecule moves
    • Vibrational - within a molecule
    • Rotational - 'spinning'
    • motions 'shut down' as temp decreases -> reach perfect order
  33. Change in Standard Molar Entropy
    deltaSo =ΣnSo (products) -ΣmSo (reactants)
  34. 0th Law of Thermo
    • Existence of equilibrium states
    • All parts of closed equilibrium system are in a state of internal/heat equilibrium
  35. 3rd Law of Thermo
    Nernst-Plank heat theorem - entropy of system goes to zero if temp goes to zero