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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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