# Exam 3 F12 - ChE 381 Exam 3 November 2 2012 Page 1 of 5 I...

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ChE 381 Exam 3 November 2, 2012 Page 1 of 5 Your Initials: I understand that academic integrity is expected of all Iowa State University Students and I pledge that I have neither given nor received unauthorized aid on this examination. Name (print) __________________________ Signature_____________________________ Date____________

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ChE 381 Exam 3 November 2, 2012 Page 2 of 5 Your Initials: 1. 30 points total What is the change in Helmholtz energy upon mixing ( A mix ) under ideal gas conditions? Express your final answer in terms of measureable properties ( i.e. V, T, P, y i ). (20 points) What general conclusions can you make about A mix ig ? Specifically, is there an expected sign for A mix ig and do you need to know the identity of the gases being mixed? Justify your answer. (10 points)
ChE 381 Exam 3 November 2, 2012 Page 3 of 5 Your Initials: 2. 35 points total What is the value of the fugacity coefficient, fugacity and residual Gibbs energy for n-hexane at T=561K, P=60 bar? T c = 510K, P c = 30 bar, = 0.300, A = 3, B = 50x10 -3 , C = -20x10

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Unformatted text preview: -6 , D = 0 ChE 381 Exam 3 November 2, 2012 Page 4 of 5 Your Initials: 3. 35 points total Given a mixture of known species A and B, explain how you would find the system composition at a specified temperature (T, K) and pressure (P, kPa). Show all relevant equations, indicate which values are known and show where you would solve for unknowns. (25 points) Note that ln A = Cx B 2 ln B = Cx A 2 where C = C 1 + C 2 *T C 1 and C 2 are known, T is in K The activity coefficient ( ) values for species A and species B are listed below for four distinct conditions. In which of these four conditions do you expect ideal Raoult’s law to give a result most similar to modified Raoult’s law? Justify your answer. (10 points) Condition A B 1 1.05 2.62 2 2.53 1.12 3 1.23 1.31 4 1.95 2.11 ChE 381 Exam 3 November 2, 2012 Page 5 of 5 Your Initials: BONUS (5 points, no partial credit) Explain why Henry’s Law is useful in modeling the implications of increasing atmospheric CO 2 levels on sealife....
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