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Unformatted text preview: roofner (bar784) Extra Credit Homework 23 Weathers (17104) 1 This printout should have 15 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 (part 1 of 2) 10.0 points Given: R = 8 . 31451 J / K mol . How much work is done by the steam when . 9 mol of water at 132 C boils and becomes . 9 mol of steam at 132 C at 1 . 6 atm pres sure? Correct answer: 3030 . 37 J. Explanation: Given : n = 0 . 9 mol , R = 8 . 31451 J / K mol , T = 132 C = 405 K , m = 18 g / mol , P = 1 . 6 atm and = 1 g / cm 3 . Using the ideal gas law, P V = nRT . m is the molar mass of water. The work done is W = P V = nRT n parenleftbigg mP parenrightbigg = (0 . 9 mol) (8 . 31451 J / K mol) (405 K) (0 . 9 mol) (18 g / mol) (1 . 6 atm) 1 g / cm 3 parenleftBig m 100 cm parenrightBig 3 1 . 013 10 5 Pa 1 atm = 3030 . 37 J . 002 (part 2 of 2) 10.0 points Find the change in internal energy of the steam as it vaporizes. Consider the steam to be an ideal gas with heat of vaporization 2 . 26 10 6 J / kg. Correct answer: 33 . 5816 kJ. Explanation: Given : L v = 2 . 26 10 6 J / kg The heat needed to vaporize the water is Q = nmL v From the first law of thermodynamics U = Q W = nmL v W = bracketleftbigg (0 . 9 mol) (18 g / mol) 1 kg 1000 g (2 . 26 10 6 J / kg) 3030 . 37 J bracketrightbigg 1 kJ 1000 J = 33 . 5816 kJ . 003 10.0 points One mole of an ideal gas is heated at constant pressure so that its temperature increases by a factor of 9. Then the gas is heated at constant temperature so that its volume increases by a factor of 9. Find the ratio of the work done during the isothermal process to that done during the isobaric process. Correct answer: 2 . 47188. Explanation: Given : k = 9 . The work done in the isobaric process is W ab = integraldisplay b a P dV = P a ( V b V a ) = nR ( k T a ) nRT a = ( k 1) nRT a , The work done in the isothermal process is W bc = integraldisplay c b P dV = nRT b integraldisplay c b dV V = nRT b ln parenleftbigg V c V b parenrightbigg = nR ( k T a ) ln k , Therefore the ratio fraction is r = W bc W ab = nR ( k T a ) ln k ( k 1) nRT a = k ln k k 1 = 9 ln(9) (9 1) = 2 . 47188 . roofner (bar784) Extra Credit Homework 23 Weathers (17104) 2 004 10.0 points The surface of the Sun has a temperature of about 6214 K.about 6214 K....
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This document was uploaded on 10/26/2011 for the course PHYS 1710 at North Texas.
 Fall '08
 Weathers
 mechanics, Work

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