Rogers Chem 1442 Exam 1

What are the four types of intermolecular attractive forces?

1. ion-dipole forces

2. dipole-dipole forces

3. london dispersion forces

4. hydrogen bonding

Dipole-dipole attractions exist between _______ molecules. Give an example

-polar

-SO2 (l)

For molecules of approximately equal molecular mass and size, dipole-dipole attractions increase with increasing ____________

polarity

What are attractive forces due to?

temporary induced dipoles

Define polarizability

refers to the ease with which the electron cloud can be distorted

Large atoms and molecules are more easily polarized than small atoms and molecules; thus, London forces ____________ with molecular size

increase

Generally, in the absence of other effects, substances consisting of large atoms and molecules will have ___________ melting points and boiling points than comparable substances which are smaller

higher

Where are dispersion forces present?

both polar and nonpolar molecules*

A hydrogen bond is an ________________ ___________ between a __________ ______________ on one molecule and a ___________________ ___________ on an adjacent molecule

-intermolecular attraction

-polarized hydrogen

-very electronegative atom

What are the three cases of hydrogen bonds?

H-F

H-O

H-N

Hydrogen bonding is responsible for?

1. higher melting point and boiling point

2. higher heat of fusion and heat of vaporization

3. higher viscosities and higher surface tension

4. lower vapor pressure

Which intermolecular attractive force is the strongest?

hydrogen bonds

Which intermolecular attractive force is the weakest?

london dispersion forces

"fusion" =

melting

Solid -> Liquid

heat of fusion

Solid -> Gas

sublimation

Liquid -> Gas

heat of vaporization

Gas -> Liquid

condensation

Gas -> Solid

deposition

Liquid -> Solid

freezing

Define heat of vaporization

the standard enthalpy change that occurs when one mole of liquid is vaporized

Define heat of fusion

the standard enthalpy change required to melt one mole of a solid

In general, the stronger the intermolecular forces the ______________ the heat of vaporization and heat of fusion

higher

For a give substance which is generally greater the heat of vaporization or the heat of fusion? Why?

-heat of vaporization

-because it takes more energy to completely separate the molecules and overcome the intermolecular attractions

What do we mean by the term "vapor"? What is the difference between a vapor and a gas?

-"vapor" is used to describe a substance in the gas phase if the gas phase is not the most stable form at that temperature and pressure

-at 25 degrees C H2O (g) = "water vapor"

at 200 degrees C H2O (g) = "water gas"

Define vapor pressure

the pressure exerted by a vapor in equilibrium with its solid or liquid state

The stronger the intermolecular attractive forces, the _________ the vapor pressure

lower

For a given liquid, vapor pressure __________ with temperature

increases

A liquid is considered volatile if it has ______________________

a vapor pressure

The stronger the intermolecular attractive forces the __________ volatile the substance

less

Define boiling point

the temperature at which the vapor press of a liquid equals the external pressure

Define normal boiling point

that temperature at which the vapor pressure of a liquid equals 760 torr

The stronger the intermolecular attractive forces the __________ the boiling point

higher

Melting point/freezing point -- temperature at which solid and liquid states are __________________

in equilibrium

The stronger the intermolecular forces, the _______ the melting point

higher

Other properties of the liquid state which are indicative of intermolecular attractive forces:

1. surface tension

2. viscosity

3. capillarity

Define critical temperature

that temperature above which it is impossible to liquify a gas

Define supercritical fluid

at Tc and Pc, the liquid and gas coalesce into a supercritical fluid

A point on a line represents:

two phases coexisting at equilibrium

Surface tension is the energy required to increase the ___________________ of a liquid

surface area

In general, the stronger the intermolecular attractive forces, the _______________ the surface tension

greater

Viscosity is a measure of the _____________________ of a liquid

resistance to flow

The stronger the intermolecular attractive forces, the _______________ the viscosity

greater

Capillary or ______________________ involves the _______________ of a liquid against the ______________________________ through a ___________________. This results from a competition between the intermolecular forces within the liquid, ________________________, and the intermolecular forces between the liquid molecules and the tube walls, ____________________________.

-capillary action

-rising

-pull of gravity

-narrow tube

-cohesive forces

-adhesive forces

Define colligative properties

properties of solutions that depend on the number of solute particles and not the identity of the solute particles

Define solution

a homogeneous mixture

Define aqueous solution

solutions with water as the solvent

Explain solute vs. solvent

-if both components were originally in the same phase, the solvent is the component in the greater amount

-if two components were in different phases, the substance that changes phases is solute

Define solubility

the amount of a substance that will saturate a given amount of a solvent at a given temperature

In a saturated solution an ________________ exists between solid solute and dissolved solute

equilibrium

Define supersaturated

a metastable state

Define miscible

two liquids that are completely soluble in each other in all proportions

Define immiscible

form two layers

Define solvation

the clustering of solvent molecules around solute particles

Define hydration

"solvation" when water is the solvent

Explain electrolytes vs. nonelectrolytes

-electrolytes dissociate into ions in aqueous solutions

-nonelectrolytes are soluble in water but they do not dissociate into ions

Explain volatile vs. nonvolatile

volatile has a vapor pressure and will evaporate

Explain "like dissolves like"

1. polar dissolves polar

2. polar dissolves ionic

3. nonpolar dissolves nonpolar

To understand the driving force in the solution process, we need to focus on three factors:

1. entropy

2. intermolecular forces

3. energetics of the solution process

Entropy can be thought of as...

a measure of the disorder of the system

When most solution forces entropy ____________

increases

Define the ******** principle

solutions form when the solute-solvent attractions are comparable in magnitude to the solute-solute attractions and the solvent-solvent attractions

Bond breaking is ___________________ and bond formation is _____________________

-endothermic

-exothermic

Another name for delta H3 is...

heat of solvation, enthalpy of solvation, heat of hydration

What is the formula for molarity (M)?

(# moles of solute)/(volume of the solution in liters)

List the six most important things about molarity

1. M x V = # moles of the solute

2. you can always replace "M" with moles/liter

3. molarity can be used as a conversion factor in dimensional analysis problems

4. molarity problems can also be solved as plug and chug (M= n/v)

5. molarity is temperature dependent

6. important shortcut: # milimoles solute = M x # mL of solution)

Molality is not ___________________. And thats why we use molality for ____________________ and __________________

-temperature dependent

-boiling point elevation

-freezing point depression

Define mass percent

(mass of solute) / (mass of solution) x 100%

What is parts per million (ppm)?

(mass solute) / (mass solution) x 10^6

What is parts per billion (ppb)?

(mass solute) / (mass solution) x 10^9

Define mole fraction (XA)

(# mol of A/total # mol )

The solubility of solids in liquids:

-often increases with temperature (but not always)

-is not greatly affected by pressure

The solubility of gases in liquids:

-decreases with increasing temperature

-is directly proportional to the partial pressure of that gas over the liquid (Henry's Law)

What are the 4 colligative properties?

1. VPL = vapor pressure lowering (Pa = XaPa)

2. BFE = boiling point elevation (delta Tb = Kb x m x i)

3. FPD = freezing point depression (delta Tf = Kf x m x i)

4. pi = osmotic pressure ( pi = MRT x i)

Define vapore pressure

the pressure exerted by a vapor in equilibrium with its liquid or solid state

The _________ the intermolecular attractive forces, the _________ the vapor pressure

-stronger

-lower

For a give liquid, vapor pressure ____________ with temperature

increases

Define volatile

easily vaporized - has a vapor pressure

Define ideal solution

a solution that obeys Rault's Law

When do you get positive deviation from Raoult's law results?

solute-solvent attractions are WEAKER compared to the solute-solute and solvent-solvent attractions

When do you get a negative deviation from Raoult's law results?

solute-solvent attractions are STRONGER than solute-solute and solvent-solvent attractions

Define semipermeable membrane

a membrane that allows small molecules and particles to pass through, but not larger molecules

Define osmosis

the net flow of solvent molecules through a semi-permeable membrane from the less concentrated side to the more concentrated side

List the four steps to using colligative properties to determine the molar mass of an unknown solute

1. determine the magnitude of the colligative effect (VPL, delta Tb, delta Tf, pi)

2. use colligative effect to calculate the concentration (delta Tb = Kb x m and pi = MRT)

3. use the definition of the concentration term to calculate the number of moles of the unknown (m= n/(mass of the solvent))

4. use the definition of molar mass (M = mass/n)

Define strong electrolytes

completely dissociate in aqueous solutions

Explain the van't Hoff i factor

i = (# mol particles in solution) / (# mol solute dissolved)

i is almost always __________ what we would expect (assuming complete dissociation)

less than

i =

observed colligative effect (calculating colligative effect assuming no dissociation)