1. Announcements 9/20/10 Demo: constant volume change (hopefully working today) Do this “Quick Writing” assignment while you’re waiting: Ralph is confused because he knows that when you compress gases, they tend to heat up (think of bicycle pumps). So, how are “isothermal” processes possible? How can you compress a gas without its temperature increasing?

2. Thought question (ungraded) How will the temperature of the gas change during this process from A to B? a. a.Increase b. b.Decrease c. c.First increase, then decrease d. d.First decrease, then increase e. e.Stay the same

3. Reading quiz (graded) What is “C V ”? a. a.heat capacity b. b.mass-pacity c. c.molar heat capacity d. d.molar heat capacity, but only for constant volume changes e. e.a detailed resumé

4. Thought question (ungraded) Which should 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.) a. a.constant volume b. b.constant pressure c. c.they are the same d. d.it depends on the temperature

5. C V and C P Constant volume change (monatomic): W = 0  E int = Q added (3/2)nR  T = Q added Compare to definition of C: Q added = nC V  T (like Q added = mc  T) C V = (3/2)R Constant pressure change a. a.What’s different? b. b.result: (monatomic) C P = (5/2)R What would be different for gases with more degrees of freedom?

6. Reading quiz (graded) What does gamma equal in the equation for an adiabatic process: a. a.C P + C V b. b.C P - C V c. c.C V - C P d. d.C V / C P e. e.C P / C V

7. Isothermal vs Adiabatic Isothermal: Adiabatic:  steeper curves for adiabatic

8. 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? (V f = V 0 /10) a. a.less than 0.1 degree C b. b.about 0.1 degrees C c. c.about 1 degree C d. d.about 10 degrees C e. e.more than 10 degrees C

9. Demo/Video Video: adiabatic cotton burner Demo: freeze spray Video: adiabatic expansion

10. Derivation of PV  (for Monatomic)  E int = Q added + W on (3/2) nR  T = -integral(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 V 5/3 = constant What’s different if diatomic?

11. 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? a. a. b. b. c. c. d. d. e. e.

12. Thought questions What would be the molar specific heat for an adiabatic process? (Hint: think of Q = nC  T.) a. a.C V b. b.C V + R c. c.C V + 2R d. d.C V - R e. e.none of the above What would be the molar specific heat for an isothermal process? (Same hint.) a. a.C V b. b.C V + R c. c.C V + 2R d. d.C V - R e. e.none of the above

13. Water/steam “saturation curve”: ideal gas?