555555555 - PY211 Lecture 23(29 Nov 2016 Temperature and...

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PY211 Lecture 23 (29 Nov 2016) Temperature and Heat [Ch. 17 Young and Freedman (cont.)] Thermal Properties of Matter [Ch. 18 Young and Freedman]
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Class info Final exam: on Friday, Dec. 16, 6:00-8:00pm – in CGS-129 – Cumulative, but including all of the new material Problem Set 9: due this Friday, Dec. 2 by 5pm. – Ten problems online. Half also submitted on paper Discussion this week: on topics from Chs. 17, 18. Lab: next week in SCI-B11 – Lab7: Conversion of Mechanical Energy to Heat Help: SCI-121 More help: on Piazza.com!
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What is an Ideal Gas? An ideal gas satisfies these conditions: – It consists of a large number of identical molecules. – The volume occupied by the molecules is negligible compared to the volume of the container. – The molecules obey Newton's Laws of Motion, and they move in random motion. – The molecules experience forces only during collisions, which are completely elastic and take a negligible amount of time.
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Worksheet Write out the ideal gas law: What is n ? What is the value of R, the universal gas constant, in SI units of J/(mol-K)? n is the number of moles. What's a mole? Let's look at molecular mass . PV = nRT n (moles) = m total (mass in grams) M (molecular mass in g/mol) R = 8.314 J/(mol K) = 0.0821 (L atm)/(mol K) A mole of anything has the same number of molecules.
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Worksheet Express the ideal gas law in terms of N , the number of gas molecules, instead of n , the number of moles. Boltzmann's constant: Avogadro's number N A is the number of molecules in one mole of any gas. Most physicists use the form: PV = Nk B T k B = R N A = 1.38 × 10 23 J/K N A = 6.02 × 10 23 = N R N A T = Nk B T PV = nRT = N N A RT
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Quiz For a given process, if n or N is constant, we can look at ratios: (A) P 2 < P 1 (B) P 2 = P 1 (C) P 1 < P 2 < 2P 1 (D) P 2 = 2P 1 (E) P 2 > 2P 1 The temperature of an ideal gas is raised from 10 o C to 20 o C while the volume is kept constant.
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