Solution to Assignment 7

Solution to Assignment 7 - SOLUTION TO HOMEWORK #7 10.1-1...

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SOLUTION TO HOMEWORK #7 10.1-1 a. In order to solve this problem, we need to know what happens at the bubble point; at this point, the first bubble is formed, so we can assume that all of the number of moles for the components in the gas phase are close to zero (yet there is an equilibrium). Therefore, we use the compositions given in the problem statement and we assume they are the compositions of the liquid. (x=z, z being the composition given). x ET = 0.05 x P = 0.10 x NB = 0.40 x MP = 0.45 Now, we know, from Raoult’s law that: y i = x i P i vap P and from the problem statement we know that the pressure is 5 bar. Therefore, we proceed to calculate the bubble point temperature. The way the bubble point temperature is done is by doing the following. We also know that: y i i = 1 and therefore, substituting 1 vap ii i i i xP y P == Therefore: 1 = x ET P ET vap + x P P P vap + x NB P NB vap + x MP P MP vap P Now, we do the following: 1 = x ET 10 A T () + B ET + x P 10 A T ( ) + B P + x NB 10 A T ( ) + B NB + x MP 10 A T + B MP P
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From this equation, we can find the bubble point temperature. This equation can be solved for the temperature, which comes out to be 294K. You can use bisection, guessing (better be clever guessing), or Goal Seek in excel. Now, we need to calculate the compositions. This is done by using Raoult’s law yielding: y ET = 0.4167 y P = 0.1730 y NB = 0.1601 y MP = 0.2502 One way of checking if the answer is correct is to use y i i = 1. If this equality is not correct, then something was done wrong. b. The dew point calculations are similar, but in this case the equations change slightly. x i = y i P P i vap also, since we are at the dew point (the point in which the first drop of liquid is formed), we can say that almost no liquid is present. 1 i i vap ii i y xP P == ∑∑ which, when the correct terms are substituted in, we obtain: 1 = P y ET 10 A T () + B ET + y P 10 A T + B P + y NB 10 A T + B NB + y MP 10 A T + B MP where we use the composition given (z) as the composition of the vapor. Solving for the
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This note was uploaded on 08/31/2011 for the course CHE 3473 taught by Professor Staff during the Spring '08 term at Oklahoma State.

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Solution to Assignment 7 - SOLUTION TO HOMEWORK #7 10.1-1...

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