Lecture_6a_4e

# Two equations govern their behavior these are derived

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Unformatted text preview: agrams at fixed pressure. Two equations govern their behavior. These are derived below. Consider a binary (two-component) system consisting of components 1 and 2. Then y1 = P1/P (Dalton’s Law) P = P1+ P2 = x1P1* + x2P2* (Raoult’s Law) (6.8) The last equation may be re-written for a binary system as P = x 1 P  + (1–x 1 )P  = P  + (P  – P  )x 1 . 2 2 2 1 1 (6.9) When pressure is lowered on a solution containing x1 mole fraction of component 1, the first bubble appears when pressure reaches the value predicted by Eq. (6.9). Therefore, this equation is called the bubble-point line equation. Substituting this expression for the total pressure in Eq. (6.8), we get x1P P1 1 y1 =  =    P 2 + (P 1 − P 2 )x 1 P 2 + (P 1 − P  )x 1 2 which gives the composition of the vapor contained in the bubble. However, it is more useful to obtain an expression for the variation of total pressure as a function of vapor composition. This is done as follows. From the equation above, we get y1P 2 (6.10) x1...
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