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Physical Chemistry > Quiz 4: Chapter 6 > Flashcards

Quiz 4: Chapter 6 Flashcards

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1
Q

What are the axes of a phase diagram?

A

pressure (y) vs temperature (x)

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2
Q

What are the phases in a phase diagram left to right?

A

Solid, liquid, gas

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3
Q

What are the three boundary lines on a phase diagram?

A

Sublimation curve - sublimation - deposition
Vapor pressure curve - vaporization - condensation
Fusion curve - melting - freezing

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4
Q

Where is the normal melting point on a phase diagram?

A

Intersection of 1 atm pressure and the fusion curve line

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5
Q

Where is the normal boiling point on a phase diagram?

A

Intersection of 1 atm pressure and the vapor pressure curve line

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6
Q

What is the general shape of the regions in a phase diagram?

A
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7
Q

What do you know about a substance when two phases are in equilibrium?

A

When two phases are in equilibrium their chemical potentials must be equal

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8
Q

What is the Clapeyron equation?

A
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9
Q

What is the Gibbs phase rule?

A

F = C - P +2
C = number of components
P = number of phases

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10
Q

What is F in the Gibbs phase rule?

A

F is the number of intensive variables (p, T) that can be changed independently without disturbing the number of phases in equilibrium

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11
Q

Give three examples of finding F.

A
  • 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
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12
Q

The majority component of a solution is called the:

A

solvent

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13
Q

The minority component of a solution is called the:

A

solute

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14
Q

How does vapor pressure of solutions change compared to pure liquids?

A
  • The vapor pressure of a solvent above a solution is lower than the pressure of the pure solvent
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15
Q

What causes vapor pressure drop above solutions?

A
  • 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
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16
Q

What is Raoult’s law (words)?

A

The vapor pressure of a volatile solvent above a solution is equal to its mole fraction of its normal vapor pressure

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17
Q

Raoult’s Law equation

A
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18
Q

When is Raoult’s law followed?

A

An ideal solution follows Raoult’s law at all compositions

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19
Q

What is the Raoult’s law graph? Axes? Direction?

A
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20
Q

What is Raoult’s law for multiple volatile components?

A
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21
Q

What is the equation for the chemical potential of the vapor above a pure liquid?

A
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22
Q

What is p*A?

A

Vapor pressure of the pure liquid. NOT the standard pressure

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23
Q

What is the chemical potential of an ideal solution?

A
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24
Q

What is Henry’s Law?

A
  • 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)
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25
Q

What is the equation for henry’s law?

A

Pvap2 = k2X2

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26
Q

What is important to know about k2?

A
  • Henry’s constant
  • is specific to a gas
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27
Q

How would you graph Henry and Raoult’s laws?

A
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28
Q

What is partitioning?

A

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

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29
Q

How does freezing point change with pressure for water?

A
  • 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
30
Q

How does freezing point change with pressure for liquids other than water?

A
  • 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
31
Q

What is a typical phase diagram vs water’s phase diagram?

A
32
Q

What is the partition coefficient?

A

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

33
Q

The hexane/water partition coefficient of phenol at 298.15 K is .20. Calculate the free energy transfer of phenol from water to hexane.

A
34
Q

Describe what a blood/gas or hexane/water partition coefficient means.

A
  • 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
35
Q

What does the hydropathy index reveal?

A
  • More positive - more hydrophobic
  • More negative - more hydrophilic
  • Mermaids are POSITIVE they are AFRAID of water
36
Q

What is equilibrium dialysis?

A

a lab method of studying the binding of a ligand (small molecule) by a macromolecule quantitatively

37
Q

What is the scratchard equation?

A
  • 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
38
Q

What is the equation for v in the Scatchard equation?

A
  • A is the ligand
  • M is the macromolecule
39
Q

What are the important components of a schatchard plot?

A
  • plot of v/[A] vs v
  • N is the x-intercept
  • K is the negative of the slope
40
Q

When given the activity of a solute in two different solvents what can you calculate?

A

We can calculate the gibbs free energy change associate taking a certain molecule from water and placing it in an aprotic solvent

41
Q

What is the equation for the free energy difference between heptane and water?

A
  • as a function of the number of carbon atoms nc
42
Q

What are the two binding patterns?

A
  • cooperative binding - the first ligand makes it easier for the next ligand to bind
  • anti-cooperative binding - each succeeding ligand is bound less strongly
43
Q

What is the binding pattern for Hemoglobin?

A
  • cooperative binding - sigmoidal shape
44
Q

Describe the binding plot of Mb and Hb.

A
45
Q

What determines liquids shapes?

A
  • 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
46
Q

What is the work of surface expansion?

A
47
Q

What is surface tension?

A
  • free energy per unit surface area or force per unit length on the surface
48
Q

Explain the Gibbs adsorption isotherm.

A
  • 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
49
Q

What is the Gibbs adsorption isotherm equation?

A
50
Q

Describe the effect of solute concentration on surface tension in water.

A
  • Ionizing salts are almost the only solutes that raise the surface tension of water
  • Almost all other solutes lower the surface tension
51
Q

How does Gibbs free energy change when accounting for the surface tension?

A
52
Q

What is the Langmuir film balance?

A
53
Q

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

A
54
Q

How does vapor pressure impact melting point and boiling point on a phase diagram?

A

Decreasing vapor pressure lowers the melting point and increases the boiling point

55
Q

Describe how boiling point elevation occurs.

A
  • The boiling point of a solution is higher than the boiling point of the pure solvent
56
Q

What is the boiling point elevation equation?

A
  • m is the molality (moles solute/ kg solvent)
57
Q

What is the freezing point depression equation?

A
58
Q

What are two examples of freezing point depression in biology?

A
  • 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
59
Q

What are colligative properties?

A

only depend on concentration not identity

60
Q

What is the equation for osmotic pressure?

A
61
Q

Which of the following has the lowest standard chemical potential at 25 degrees celsius? (CH4) g, l, s, aq

A
  • 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
62
Q

What is important about Kh?

A

lower values mean higher solubility

63
Q

What can be inferred from Henry’s law?

A

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.

64
Q

What is surface excess concentration?

A

The surface excess concentration Γ is the area-related concentration of a surfactant at the surface or interface. It has the unit mol/m2

65
Q

What is a surfactant?

A

Surfactants are chemical compounds that decrease the surface tension

66
Q

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?

A

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

66
Q

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?

A

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

67
Q

Describe delta G at boiling point

A

At the normal boiling point the vapor and the liquid are at equilibrium so delta G = 0

68
Q

Why is the entropy of vaporization of ammonia higher than predicted for liquids?

A

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

69
Q

What is important to remember for boiling point elevation and FP depression?

A

If the solute is a salt then it must fully dissociate to realize the full depression/elevation (moles solute*2 molecules/ kg solvent) = molality

Physical Chemistry (6 decks)

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