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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
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saturation pressure
pressure at which the liquid and vapor phases are in equilibrium at given temp
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saturation temperature
the temperature at which the liquid and vapor phases are in equilibrium at given pressure
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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
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moisture
1 - x, where x is quality x, or mg/mg+mf
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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
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superheated
given tempreature is greater than the saturation temp for given pressure
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compresed liquid
when the pressure is greater than the saturation presure at a given temp
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How to choose the right table
Compare the known state properties to the properties in the saturation region
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compressed liquid region
v < vf
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saturation region
vf < v < vg
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superheated region
vg < v
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equations of state
relationship between the state variables, temperature, pressure, and specific volume
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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
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Gas constant R
- R = Ru/M
- Ru is universal gas constant
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mass
m = NM, the number of moles times the molar mass
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Combined gas law
- Ideal gas for a fixed mass - m1 = m2, or
- PV/RT (1) = PV/RT (2)
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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.
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State function
of energy - value depends on final and initial states, not on internal energy used
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Chemical potential
proportionality constant m; change in internal energy is proportional to the number of particles dn added to the styem
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Combined 1st and 2nd laws
dU = TdS – PdV + mdn
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Kelvin Statement
It is not possible for the absorption of heat from a reservoir to complete convert to work
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Entropy
- measure of dispersal of energy (molecular disorder)
- Non-conserved property; as entropy increases, it increases entropy of universe
- Increases as DOF increases
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Isentropic
- Entropy does not change (either by heat transfer or irreversibilities)
- Or, reversible adiabatic process
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Reversible Process
ability to run a process back and forth infinitely without losses (i.e. perfect pendulum, mass on string, etc.)
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Irreversible Process
- i.e. dropping clay, hammering a nail, breaking glass
- Sources; friction, pressure, voltage, temp, and concentration drops
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adiabatic
- no heat is gained or lost in a system
- q=0
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Engineering devices
work best when isentropic and irreversibilities are eliminated
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Disorder
naturally increases, and natural processor proceed spontaneously to order
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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
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spontaneous
- process that occurs without ongoing outside intervention
- i.e. ice melting at room temperature, expansion of gas in space
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Molecular motion
- Translational - entire molecule moves
- Vibrational - within a molecule
- Rotational - 'spinning'
- motions 'shut down' as temp decreases -> reach perfect order
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Change in Standard Molar Entropy
deltaSo =ΣnSo (products) -ΣmSo (reactants)
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0th Law of Thermo
- Existence of equilibrium states
- All parts of closed equilibrium system are in a state of internal/heat equilibrium
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3rd Law of Thermo
Nernst-Plank heat theorem - entropy of system goes to zero if temp goes to zero
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