Quiz 4: Chapter 6 Flashcards
What are the axes of a phase diagram?
pressure (y) vs temperature (x)
What are the phases in a phase diagram left to right?
Solid, liquid, gas
What are the three boundary lines on a phase diagram?
Sublimation curve - sublimation - deposition
Vapor pressure curve - vaporization - condensation
Fusion curve - melting - freezing
Where is the normal melting point on a phase diagram?
Intersection of 1 atm pressure and the fusion curve line
Where is the normal boiling point on a phase diagram?
Intersection of 1 atm pressure and the vapor pressure curve line
What is the general shape of the regions in a phase diagram?
What do you know about a substance when two phases are in equilibrium?
When two phases are in equilibrium their chemical potentials must be equal
What is the Clapeyron equation?
What is the Gibbs phase rule?
F = C - P +2
C = number of components
P = number of phases
What is F in the Gibbs phase rule?
F is the number of intensive variables (p, T) that can be changed independently without disturbing the number of phases in equilibrium
Give three examples of finding F.
- If the point (p and T point of a phase diagram) lies on a phase boundary line, then if you change temperature the pressure cannot be independently varied without changing the number of phases. F = 1
- If the point (p and T point of a phase diagram) lies in the middle a phase area, P and T can both be independently varied and F = 2
- If the point is the triple point F = 0
The majority component of a solution is called the:
solvent
The minority component of a solution is called the:
solute
How does vapor pressure of solutions change compared to pure liquids?
- The vapor pressure of a solvent above a solution is lower than the pressure of the pure solvent
What causes vapor pressure drop above solutions?
- The solute particles replace some of the solvent molecules at the surface
- Solute molecules hinder the escape of solvent molecules but not their return
- Eventually equilibrium is re-established but a smaller number of vapor molecules - therefore the vapor pressure will be lower
What is Raoult’s law (words)?
The vapor pressure of a volatile solvent above a solution is equal to its mole fraction of its normal vapor pressure
Raoult’s Law equation
When is Raoult’s law followed?
An ideal solution follows Raoult’s law at all compositions
What is the Raoult’s law graph? Axes? Direction?
What is Raoult’s law for multiple volatile components?
What is the equation for the chemical potential of the vapor above a pure liquid?
What is p*A?
Vapor pressure of the pure liquid. NOT the standard pressure
What is the chemical potential of an ideal solution?
What is Henry’s Law?
- Addendum to Raoult’s law for REAL solutions
- For real solutions at low concentrations the vapor pressure is still proportional to the mole fraction of the substance but the constant of proportionality is not standard pressure
- the constant of proportionality is k2 (Henry’s constant)
What is the equation for henry’s law?
Pvap2 = k2X2
What is important to know about k2?
- Henry’s constant
- is specific to a gas
How would you graph Henry and Raoult’s laws?
What is partitioning?
Partitioning is the distribution of a solute between two immiscible phases (ie between two liquids or a liquid and a solid)
- Immiscible = not forming a homogenous mixture when added together