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
How does freezing point change with pressure for water?
- Freezing point decreases with pressure for water (water will freeze at a lower temperature)
- This is a consequence of ice being less dense than water
- When there is greater pressure the water is more likely to stay a liquid because it is more dense
How does freezing point change with pressure for liquids other than water?
- Freezing point increases with pressure (the substance will freeze at a higher temperature)
- This is because the liquid is less dense than the solid
- When there is greater pressure the substance is more likely to remain a solid because it is more dense
What is a typical phase diagram vs water’s phase diagram?
What is the partition coefficient?
The ratio of activities is called the partition coefficient and it can be used to determine the free energy transfer of a solute from phase 1 to phase 2
The hexane/water partition coefficient of phenol at 298.15 K is .20. Calculate the free energy transfer of phenol from water to hexane.
Describe what a blood/gas or hexane/water partition coefficient means.
- the blood/gas partition coefficient of a general anesthetic measures how easily the anesthetic passes from gas to blood
- the hexane/water partition coefficient measures how easily a solute passes from water to hexane
What does the hydropathy index reveal?
- More positive - more hydrophobic
- More negative - more hydrophilic
- Mermaids are POSITIVE they are AFRAID of water
What is equilibrium dialysis?
a lab method of studying the binding of a ligand (small molecule) by a macromolecule quantitatively
What is the scratchard equation?
- v = average number of molecules of A bound to the macromolecule
- N = number of binding sites on the macromolecule
- [A] = concentration of free A, the same inside and outside of the bag
- K = equilibrium constant
What is the equation for v in the Scatchard equation?
- A is the ligand
- M is the macromolecule
What are the important components of a schatchard plot?
- plot of v/[A] vs v
- N is the x-intercept
- K is the negative of the slope
When given the activity of a solute in two different solvents what can you calculate?
We can calculate the gibbs free energy change associate taking a certain molecule from water and placing it in an aprotic solvent
What is the equation for the free energy difference between heptane and water?
- as a function of the number of carbon atoms nc
What are the two binding patterns?
- cooperative binding - the first ligand makes it easier for the next ligand to bind
- anti-cooperative binding - each succeeding ligand is bound less strongly
What is the binding pattern for Hemoglobin?
- cooperative binding - sigmoidal shape
Describe the binding plot of Mb and Hb.
What determines liquids shapes?
- liquids shape to minimize their surface area
- work is require to create surface area, and therefore liquids minimize their surface area
- the energy of a molecule at the surface is higher than one in bulk
- liquids tend to be spherical - the sphere has the lowest surface to volume ratio
What is the work of surface expansion?
What is surface tension?
- free energy per unit surface area or force per unit length on the surface
Explain the Gibbs adsorption isotherm.
- substances that lower the surface tension concentrate at the surface and give large decreases in surface tension
- substances that raise the surface tension avoid surfaces and give only small increases in surface tension
What is the Gibbs adsorption isotherm equation?
Describe the effect of solute concentration on surface tension in water.
- Ionizing salts are almost the only solutes that raise the surface tension of water
- Almost all other solutes lower the surface tension
How does Gibbs free energy change when accounting for the surface tension?
What is the Langmuir film balance?
Calculate the work needed to raise a wire of length l and to stretch the surface of a liquid through a height h. Ignore the gravitational potential energy and assume a constant surface tension
How does vapor pressure impact melting point and boiling point on a phase diagram?
Decreasing vapor pressure lowers the melting point and increases the boiling point
Describe how boiling point elevation occurs.
- The boiling point of a solution is higher than the boiling point of the pure solvent
What is the boiling point elevation equation?
- m is the molality (moles solute/ kg solvent)
What is the freezing point depression equation?
What are two examples of freezing point depression in biology?
- Rainbow smelt - produces glycerol and other molecules to protect the water in its cells from freezing
- Spring pepper frog - cold temperatures trigger a breakdown of the polysaccharide to glucose monomers that enter the bloodstream of the frog to protect against freezing
What are colligative properties?
only depend on concentration not identity
What is the equation for osmotic pressure?
Which of the following has the lowest standard chemical potential at 25 degrees celsius? (CH4) g, l, s, aq
- The chemical potential is the rate of change of free energy of the system with respect to the number of atoms or molecules being added into the system
- For gaseous methane the change of free energy of a system is negligibly small at 25 degrees celsius so the chemical potential of the gas is the least
What is important about Kh?
lower values mean higher solubility
What can be inferred from Henry’s law?
The Henry’s law constants are increasing with increasing temperature for most gases which by Henry’s law means that the solubility of a gas is decreasing with increase in temperature.
Therefore, the value of the free energy is continuously increasing (becoming more positive) with increasing temperature.
What is surface excess concentration?
The surface excess concentration Γ is the area-related concentration of a surfactant at the surface or interface. It has the unit mol/m2
What is a surfactant?
Surfactants are chemical compounds that decrease the surface tension
Solutes raise the boiling points of solutions. If a solute forms complexes in the solvent how will this affect the change in boiling point? Will the boiling point increase more or increase less when a solute forms complexes?
The boiling point will increase less if the solute forms complexes in the solvent because the concentration of urea will be less than the actual concentration
Solutes raise the boiling points of solutions. If a solute forms complexes in the solvent how will this affect the change in boiling point? Will the boiling point increase more or increase less when a solute forms complexes?
The boiling point will increase less if the solute forms complexes in the solvent because the concentration of urea will be less than the actual concentration
Describe delta G at boiling point
At the normal boiling point the vapor and the liquid are at equilibrium so delta G = 0
Why is the entropy of vaporization of ammonia higher than predicted for liquids?
There is hydrogen bonding in liquid ammonia that hinders translation/rotation so energy is dispersed over lower levels, decreasing the entropy of the liquid relative to that of the gas
What is important to remember for boiling point elevation and FP depression?
If the solute is a salt then it must fully dissociate to realize the full depression/elevation (moles solute*2 molecules/ kg solvent) = molality
