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Announcements 1/26/11. Prayer Please do this “Quick Writing” assignment while you’re waiting for class to start:

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Announcements 1/26/11

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Announcements 1 26 11

Announcements 1/26/11

  • Prayer

  • Please do this “Quick Writing” assignment while you’re waiting for class to start:

    Ralph is confused because he knows that when you compress gases, they tend to heat up (think of a bicycle pump nozzle getting hotter as you force the gas from the pump to the tire). So, how are “isothermal” processes possible? How can you compress a gas without its temperature increasing?


Announcements 1 26 11

Demo

  • Constant volume change, aka “alcohol rocket”


Thought question

Thought question

  • How will the temperature of the gas change during this process from A to B?

    • Increase

    • Decrease

    • First increase, then decrease

    • First decrease, then increase

    • Stay the same


Reading quiz

Reading quiz

  • What is “CV”?

    • heat capacity

    • mass-pacity

    • molar heat capacity

    • molar heat capacity, but only for constant volume changes

    • your “curriculum vitae”, a detailed resumé


Thought question1

Thought question

  • Which will be larger, the molar heat capacity for constant volume changes or the molar heat capacity for constant pressure changes? (Hint: Think of the First Law.)

    • constant volume

    • constant pressure

    • they are the same

    • it depends on the temperature


C v and c p

CV and CP

  • Constant volume change (monatomic):

    W = 0

    Eint = Qadded

    (3/2)nRT = Qadded

    Compare to definition of C: Qadded = nCVDT

    CV = (3/2)R (monatomic)

  • Constant pressure change

    • What’s different?

    • result: CP = (5/2)R (monatomic)

  • What would be different for gases with more degrees of freedom?


Reading quiz graded

Reading quiz (graded)

  • What does gamma equal in the equation for an adiabatic process:

    • CP + CV

    • CP - CV

    • CV - CP

    • CV / CP

    • CP / CV


Isothermal vs adiabatic

Isothermal vs Adiabatic

  • Isothermal:

  • Adiabatic:

     steeper curves for adiabatic


Thought question2

Thought question

  • How much do you think the temperature of the air in this room would change by if I compressed it adiabatically by a factor of 10? (Vf = V0/10)

    • less than 0.1 degree C

    • about 0.1 degrees C

    • about 1 degree C

    • about 10 degrees C

    • more than 10 degrees C


Demo video

Demo/Video

  • Demo: freeze spray

  • Video: adiabatic expansion

  • Demo: adiabatic cotton burner


Derivation of pv g for monatomic

Derivation of PVg (for Monatomic)

Eint = Qadded + Won

(3/2) nRT = - PdV

(3/2) nRdT = -PdV

(3/2) nR d(PV/nR) = -PdV

(3/2) (PdV + VdP) = -PdV

(3/2) VdP = -(5/2) PdV

dP/P = -(5/3) dV/V

lnP = (-5/3)lnV + constant

lnP = ln(V-5/3) + constant

P = constant  V-5/3 (it’s a different constant)

P V5/3 = constant

What’s different

if diatomic?


Thought question3

Thought question

  • Which of the curves on the PV diagram below is most likely to represent an isothermal compression, followed by an adiabatic expansion back to the initial volume?


Thought questions

Thought questions

  • What would be the molar specific heat for an adiabatic process? (Hint: think of Q = nCDT.)

    • CV

    • CV + R

    • CV + 2R

    • CV - R

    • none of the above

  • What would be the molar specific heat for an isothermal process? (Same hint.)

    • CV

    • CV + R

    • CV + 2R

    • CV - R

    • none of the above


Water steam saturation curve ideal gas

Water/steam “saturation curve”: ideal gas?


Water steam saturation curve ideal gas1

Water/steam “saturation curve”: ideal gas?


Water steam saturation curve ideal gas2

Water/steam “saturation curve”: ideal gas?


Water steam saturation curve ideal gas3

Water/steam “saturation curve”: ideal gas?


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