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Unformatted text preview: e the mixture is still proportional to the mole fraction of B in the mixed liquid. However, the constant of proportionality, which we will denote kH(B/A) is not the partial pressure of pure B, it is either lower or larger than PB*. In this case, we say that the Marand’s Notes: Chapter 5  The Properties of Simple Mixtures 171 solute (minor component in the mixture) follows Henry’s law and the constant, kH(B/A) is called Henry’s constant for B diluted in A. P P A*
PB* P RL(A)
RL(B) PA
kHB/A PB kHA/B HL(A) HL(B) xA = 0 xA = 1 xA Similarly, when B is almost pure (solvent) and A is very dilute (solute), then the partial pressure of A is still proportional to the mole fraction of A in the mixed liquid and the proportionality constant is called the Henry’s constant for A diluted in B. Such behavior can be easily represented on diagrams of partial pressure versus mole fraction. Note that there is no reason to expect that the range of mole fractions where A obeys Raoult’s law be identical to that where B obeys Henry’s law. Same thing for B obeying Raoult’s law and A obeying Henry’s law. Marand’s Notes: Chapter 5  The Properties of Simple Mixtures 172 When component A obeys Raoult’s law, then PA = xA PA* When component A does not obey Raoult’s law, we know P A ≠ xA PA*. So we define a new quantity γA called the activity coefficient for A in the mixture of composition xA such that P A = γA xA PA* (a similar approach was used for the fugacity coefficient). This quantity describes the departure from Raoult’s law for A. When A obeys...
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 Spring '07
 AREsker
 Physical chemistry, pH

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