12 Questions
Explain the difference between ideal and non-ideal solutions in terms of molecular interactions.
Ideal solutions have no interactions between molecules, while non-ideal solutions involve interactions between molecules.
What is the significance of ∆u in determining the behavior of solutions?
∆u determines how solutions depart from ideality.
How does ∆H differ in ideal and non-ideal solutions?
In non-ideal solutions, ∆H is approximately equal to ∆U, while in ideal solutions, there is no enthalpy change.
Describe positive deviations in solutions and their effect on mixing.
Positive deviations indicate that mixing is energetically not favorable, leading to non-ideal behavior.
What determines how solutions depart from ideality?
The difference in molecular interactions, specifically ∆u, determines how solutions depart from ideality.
Explain the formula for ∆Gmix in non-ideal solutions.
∆Gmix = n ∆u + nRT ( xA ln xA + xB ln xB )
What is the condition for a positive deviation from Raoult's Law?
pCS = pB*
Explain why mixing acetone and chloroform results in a negative deviation from Raoult's Law.
H-bonding attraction
What is the condition for an ideal dilute solution according to the text?
xCS2 = xB → 1
When does Henry's Law apply in the context of ideal dilute solutions?
xB → 0 (B is the 'solute')
What does the Henry's Law constant, KB, depend on?
Solvent/solute mixture and temperature
What is the consequence of a positive deviation in Henry's Law?
KB > pB*
Study Notes
Two-Component Phase Equilibria III
Ideal Solutions
- Free energy change in ideal solutions: ∆Gmix = nRT ( xA ln xA + xB ln xB )
- ∆Gmix is purely entropic, similar to gas mixtures
- No enthalpy change (∆Hmix = 0) and no volume change (∆Vmix = 0)
Non-Ideal Solutions
- Molecular interactions: uAA, uBB, and uAB determine the deviation from ideality
- ∆u = 2uAB - (uAA + uBB) determines how solutions depart from ideality
- Positive deviations: ∆u > 0, mixing is energetically not favorable
- Negative deviations: ∆u < 0, mixing is energetically favorable
Deviations from Raoult's Law
Positive Deviations
- Example: acetone and carbon disulphide
- ∆Gmix > ∆Gmix (ideal)
- Vapor pressure is higher than expected by Raoult's Law
Negative Deviations
- Example: acetone and chloroform
- ∆Gmix < ∆Gmix (ideal)
- Vapor pressure is lower than expected by Raoult's Law
Ideal Dilute Solutions and Henry's Law
Ideal Dilute Solution
- Defined by limits xB → 1 and xB → 0
- Raoult's Law applies for the solvent (xB → 1)
- Henry's Law applies for the solute (xB → 0)
Henry's Law
- pCS = xCS KCS
- KB is the Henry's Law constant, dependent on the solvent/solute mixture and temperature
- Positive deviation: KB > pB*
- Negative deviation: KB < pB*
Test your knowledge on Two-Component Phase Equilibria III, Ideal and Non-Ideal Solutions, and Free energy change in ideal solutions. Explore concepts related to ∆Gmix and its calculation in different liquid solutions.
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