Chemistry C2407x First Exam, Exams of Optics

Download Chemistry C2407x First Exam and more Exams Optics in PDF only on Docsity! Columbia University in the City of New York New York, N.Y. 10027 Chemistry C2407x 2002 First Exam George Flynn September 26, 2002 Total Points: 150 75 Minutes All questions are NOT weighted equally. I have attempted to order the questions from the least difficult to the most difficult, but "beauty is in the eye of the beholder", so skip around to find the problems that are easiest for you. Good luck! Please print your name in the boxes provided and sign where indicated. Tear off this sheet and pass it to the right for the proctors to pick up. Print your last name: Print your first name: Signature:_____________________________________________ Columbia University in the City of New York New York, N.Y. 10027 Chemistry C2407x 2002 First Exam George Flynn 2 September 26, 2002 Total Points: 150 75 Minutes All questions are NOT weighted equally. I have attempted to order the questions from the least difficult to the most difficult, but "beauty is in the eye of the beholder", so skip around to find the problems that are easiest for you. Good luck! Please print your name in the boxes provided. Print your last name: Print your first name: Do not write anything else on this page. Answer the questions in the spaces provided on the following pages. 1a 2a 3a 4a 1b 2b 3b 4b 1c 3c 4c 1d 3d 4d 3e 3f Print your name here: Problem 1: (35 points) [Oxtoby Problems 4.41-4.43] a)(10 points) Compute the root-mean-square speed of H2 molecules in hydrogen gas at a temperature of 300 °K. The molecular weight of H2 is 2 gm/mole. Show all reasoning clearly. 5 b)(10 points) Imagine now that the sample of 2.00 moles of N2 gas and 1.00 moles of He gas is transferred to a cylindrical container with a moveable, frictionless piston that holds the gas at a constant pressure of 2.00 atm. Determine the heat absorbed by this sample if its temperature is raised from 350 to 400 °K at constant pressure. Show all reasoning clearly. Print your name here: Problem 3: (50 Points) A 1.0 liter bulb is evacuated until the pressure of gas inside the bulb is negligible. Unfortunately, there is a hole in the bulb that allows air to leak into the bulb and the pressure to rise to 1.00×10-6 Atm after 1.00 hour. In what follows, use exact kinetic theory formulas from the free formula sheet. You may assume that the surrounding atmosphere of gas is pure N2 (MW=28 gm/mole) at one atmosphere pressure and that the temperature is constant at 275 °K. The pressure of the gas surrounding the bulb never changes because the volume of the surroundings is infinite compared to the volume of the bulb. a) (5 points) Determine the average speed of N2 molecules in this problem. Show all reasoning clearly! b) (10 points) What is the number density ρ s (number of molecules/cm3), of N2 molecules in the surrounding atmosphere? Show all reasoning clearly. 6 Print your name here: c) (5 points) What is the number density ρb (number of molecules/cm3), of N2 molecules in the bulb at the end of one hour? Show all reasoning clearly. d) (10 points) To be exact, N2 molecules effuse into the bulb and once inside can effuse out again. By considering the ratio of (the constant rate of effusion in) to (the maximum rate of effusion out) during the one hour leak time, show that effusion out of the bulb can be safely neglected. Show all reasoning clearly. 7 Print your name here: e)(10 points) Determine the rate (molecules/sec) at which molecules leak into the bulb over the 1 hour period from the data given. Show all reasoning clearly. f) (10 points) What is the area of the hole in the bulb through which the gas leaks? Show reasoning clearly.