AnswerKey_Quiz3_Fall2008_1

AnswerKey_Quiz3_Fall2008_1 - Quiz #3 Chem 3615- Physical...

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Unformatted text preview: Quiz #3 Chem 3615- Physical Chemistry Instructor: Esker September 18, 2008 NAME:_____Answer Key________ Score = 40 + _______x15 = _______ Useful Information: pV = nRT, R = 8.314 Jmol-1K-1 = 0.08206 Latmmol-1K-1, 1 atm = 760 mm Hg = 760 Torr = 101325 Pa, 0.001 m3 = 1 L = 1000 cm3, dW = - Fdz = -popdV, Euler's Formula x y z 1 V 1 V nRT an 2 , dU = dQ + dW, H = U + pV, = -1 , p = , = - , =- y z (V - nb ) V 2 V p T V T p z x x y T U H -1 CV = = constant, pV = constant, p1- T = , Cp = , JT = , dS = dQ/T, TV p T V T p H constant, = Cp/Cv, G = H-TS, A = U-TS Circle the correct letter. If you change your mind, make sure the original answer is completely erased. If you are using a pen, black out a wrong answer completely 1. Consider the following equation of state where b > 0 and constant: Indicate which of the following statements must be true or that all of the above are false. (a) The gas has no attractive interactions (c) The coefficient of thermal expansion is 1/T (e) All of the above are false (b) The gas has a Boyle temperature (d) The isothermal compressibility is 1/p (a) From the expression of p, we see this is just the repulsive part of the van der Waals equation of state. If we compare this with an ideal gas, the denominator for the real gas is smaller leading to larger pressures. Indeed, this gas has no attractive interactions so (a) is true. ANSWER = A (b) Looking at the expression for Z, we see that Z > 1 for all T as B' > 0 for all T and only approaches 1 in the limit of infinite temperature so this gas does not have a Boyle temperature, so (b) is false. (c) (d) Page 1 of 3 2. Consider the following equation of state where a > 0 and b > 0 are constants: 2 What is the Boyle temperature? (a) (b) (c) (d) (e) , 3. Indicate which of the following functions is not an exact differential or that all of the above are exact. (a) (c) (e) All of the above are exact (b) (d) Page 2 of 3 Answer = E 4. Consider the graph of pressure vs. molar density for an isotherm of a real gas where the temperature is above the triple point temperature. Which of the following must be false? (a) Point U is in the one-phase gas state. True the low pressure, low density region should be the one-phase gas state. (b) Point Y corresponds to the molar density of the gas in the two-phase region. False, Y corresponds to the molar density of the liquid in the two-phase region. (c) At Point W, there is more gas than liquid in the two-phase mixture. True, lever rule tells us that the closer we are to an end point the more of that phase we have. As W is closer to V (molar density of the gas in the two phase region), we have more gas than liquid. (d) Point Z is in the one-phase liquid state. True, for densities greater than the molar density of the liquid for the two-phase region, we be in the one-phase liquid state. (e) T < critical temperature True, in order to have a liquid, we must be below Tc. Page 3 of 3 ...
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