3400-exam2-solns

3400-exam2-solns - Exam 2 CHM 3400 Dr Chatfield Read...

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Unformatted text preview: Exam 2 CHM 3400, Dr. Chatfield, Read through the questions thoroughly, set up the answers carefully, show your work, and be neat. There are 5 questions; each is worth 20 points. Partial credit will be given when the instructor can follow your train of thought. Credit will not be given for answers without work or reasoning. If you have difficulty with a question, go on and return to it later. Check your work. GOOD LUCK! 1. An aqueous solution of an unknown compound is prepared by dissolving 0.0500 g of the unknown in water so that the total volume of the solution is 100.0 mL. The osmotic pressure at 298 K is measured to be H = 76.0 Torr. Determine the molar mass It 0 l7, 2 5‘ I? é ’- oftheunkown. Ida ' 7— '7é’oTor/ ‘ 7LDDI/ Q4”? [‘33]: WT ‘ o,g£3/qq7 L—lacer R (my? 179/4 2 <9. 00 V0967 ”ml/L V: a/w L , A 0%067 my! to“ vCBJ - 5,90 5790 _ n 5 ' . 11— " W - (Zia/MA” M 2 I4 “" 0. 00a 2. Determine the boiling point of methanol in a rotovap in which the pressure is 0.500 ‘bar. Given: The standard boiling point of methanol (Le. Tb at p = 1 bar) is 337.2 K, and AmpHo = 35.27 kJ mol'l. (You may treat AvapHo = 35.27 as constant.) 9 atf= git-’1‘ (“J—FA?) L/avfl‘lww 3. Below is a phase diagram for a binary liquid-gas mixture. Answer questions a—e; each :is worth 4 points. , a. Label the l-phase and 2-phase regions of the phase diagram. . If a mixture with composition XA = 0.6 is heated, at what temperature will boiling begin, i.e. vapor begin to form a a (estimate from the plot)? 5— 4 For heating process, described in (b), what will the composition of the vapor H be (xA = '2) when boiling just begins? X4: 0. 0% . What is a mixture with composition XA = 0.4 called? Q are 0 Tag/4A» Is it possible to separate the components by distillation beginning with a mixture with composition 'XA=0.4? Why or why not? W0, LRZ‘MJMWB f/Lwcc, A M S W_cmc_%/;"w/I'm fi) Qéao 79W wifo/‘e Lox/s, 4. In class and or; homework, we saw how to predict cooling curves from a given phase diagram. In this question, we turn the problem around,_ and see how a set of cooling curVes can be used to construct a phase diagram. Below is a set of cooling curves obtained for a mixture of two metals, A and B. At the highest temperature, there is one phase and it is liquid. At the lowest temperature, the mixture is solid. (a) From the cooling curves, construct the phase diagram on the graph provided. Cooling Curves 23:00 25:0-02 23:0-2 25:0'4 ZB=0-6 ZB=0.8 23:0.98 ZB=1.0 1200 1000 800 T (°C) 600 400 200 0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 time (arbitrary units) III'MI :iill n!!! (b) Identify the eutectic composition (23 = ?) Q E a 0 , é (c) When the overall composition (23) is 0.4 and the temperature is 600 °C: i. Determine the composition of the liquid (X13) and solid (YB) phases present ii. Determine the relative amount of the liquid and solid phases (nl/ns) 5. Consider a rigid container as sketched below. It is divided into two sections of equal ,‘ volume by a partition. Initially, there is 1 mol 02 on one side at 1 bar pressure, and a ' mixture of 1 mol 02 and 2 mol N; on the other side at 3 bar pressure. At a particular time, the partition is removed. Calculate AS, the change in entropy after the partition is removed. You may treat the gases as perfect. Hint: construct a cycle, that is, a series of fictitious steps. ‘ lmol 02+ 2 mol N2 LC‘é-‘f m/K/ ‘9LI‘WL gw 12/39 valunie”. Mayfaéfim} ‘7” 1' A ,(Lpf akamuézzv AS“: 2 A53 2 H.623 M” l I . w‘ I~ [55’ )0 623 wealtd C1799 hefl,% Jl/aw => 495%» :0) Afw>A9) Equations and constants for Exam 2, CHM 3400, Fall 2011 l'atm = 760 Torr = 1.01325 bar R = 8.31451 J K'1 mol'1= 0.0831451 L bar K'l mol" H = [B]RT ATf = Kth ATb = KbbB AG = nRT(xA1nXA-+ XBIan) AS = -nR(xAlnxA + XBII’IXB) Vf AS = nR 1n —— K. . A H0 mi = ””P (i _ i) p R T 7" AG = -SmAT AG = VAp ArGO = -RT In K AH = CpAT ArH(T’) = ArH(T) + ACPAT AS = Cp ln[£] T1 dU = TdS — pdV F = C — P + 2 M = XApA* p3 = XBKB G = ”AM + ”3/13 ,uA =,uff +RTlnaA n' — [H n” [I ...
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