Download Thermodynamics: Work & Heat Transfer in Helium Balloon's Isothermal Expansion and more Study notes Physics in PDF only on Docsity! Outline Equipartition of energy Work and volume change First Law of thermodynamics Adiabatic expansion Problem 8-22/23 A balloon contains 3 moles of helium at sea level where p=101 kPa. It rises to the stratosphere where p=30 kPa, while maintaining a constant 300 K temperature. How much work is done during this isothermal expansion? How much heat flowed into the balloon from outside? First Law of Themodynamics Change in internal energy (change in temperature) Heat transferred TO the system Is work done BY the system Fundamental Derived U=Q−W=Q−pdV U Q W U=nCvT Q=nCvT Molar specific heats c (J/kg K) M (kg/mol) C (J/mol K) Al 910 0.027 24.6 Cu 390 0.064 24.8 Pb 130 0.207 26.9 H20 4190 0.018 75.4 He 3120 0.004 12.5 Ar 312 0.040 12.5 H2 10000 0.002 20.4 Equipartition of energy (section 18.3) All materials have an internal energy of R=8.4 J kg⋅K R=kBNA Uinternal= 1 2 kBT degree of freedom U= 1 2 dkBNT Cv= 1 2 d×R
(a)
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AW = pAVis the work
done when the volume
increases by AV... ... and the work
i done going from
V, to V, is the area
*,_under the entire curve.
This pV–diagram shows two isotherms for the same amount of an ideal gas. Which isotherm corresponds to the higher temperature? A. curve #1 B. curve #2 C. answer depends on the particular temperatures in question D. answer depends on the particular quantity of gas E. both C. and D. are correct Q18.2 1st Law of Themodynamics -- Interp. As ever, be careful to identify the system. Applies to all systems, but some more useful than others. First law is really a statement of conservation of energy. U can be temperature OR chemical (nuclear, electrical) energy W is ALWAYS mechanical work Q is ALWAYS heat W is “useful” energy Heat is either wasted, or can only be used with some limited efficiency. Heat can be conducted, radiated or convected. Education and independence of mind Imagination is more important than knowledge. -- Albert Einstein He who has imagination without learning has wings but no feet. -- Joseph Joubert To invent, you need a good imagination and a pile of junk. -- Thomas Edison If you want to get laid, go to college. If you want an education, go to the library. -- Frank Zappa Heat Transfer You can remove heat from an object by conduction, convection, or radiation. conduction radiation H= Q t =−kA T x P=H= AT4 =5.67×10−8 W m2K4
