CHEM 122 Chp 11.

Intermolecular Forces
The attractive forces that exist among the particles that compose matter.
Thermal Energy
The energy associated with the movement of molecules and atoms.
Crystalline Solids
Crystalline Solids
Atoms and molecules are composed in 3D. (Ordered Structure)
Amorphous Solids
Amorphous Solids
Atoms and molecules have no long-range order.
Dispersion Force
Weakest Force: Exhibited in all molecules and atoms. Result of fluctuations in electron distribution.
Which halogen has the highest boiling point?

Cl2
Br2
I2

I2
Polar Molecules
A partial negative charge and a complementary positive charge. Asymmetric.
Miscibility
The ability to mix without separating into two states.
What kind of molecule is miscible with water?
A polar molecule.
Which molecules have dipole forces?

CO2
CH2Cl2
CH4

CH2Cl2
Which molecules have dipole-dipole forces?

Cl4
CH3Cl
HCl

CH3Cl
HCl
Hydrogen Bonding
When H is bonded with N, O or F.
Rank from highest IM force to lowest.

Dipole-Dipole
Dispersion
Hydrogen Bonding

Hydrogen Bonding ->
Dipole-Dipole ->
Dispersion
Ion-Dipole Force
When an ionic compound is mixed with a polar compound. (Aqueous solutions).
Which substance has the highest boiling point?

CH3OH
CO
N2

CH3OH
How many hydrogen bonds does Thymine and Adenine have?

Cytosine and Guanine?
(DNA)

3

2

Surface Tension
The energy required to increase the surface area by a unit amount.
As IM forces decrease, surface tension…..

decreases
increases
stays the same

Decreases
Viscosity
The resistance of a liquid to flow.
Substances have greater viscosity when they have ________ IM forces.

Higher
Lower

Higher
Viscosity increases as molecule size _________________.

Increases
Decreases

Increases
What SAE oil would a car need for the summer?
A high SAE number oil.
Capillary Action
The ability of a liquid to flow against gravity up a narrow tube.
What two forces result in capillary action?
Adhesive forces and cohesive forces.
Adhesive Forces
The attraction between molecules and the surface of a tube.
Cohesive Forces
The attractions between the molecules themselves.
Vaporization
The transition of a liquid to a gas.
Condensation
The transition of a gas to a liquid.
______________ IM forces cause a higher evaporation rate.

Stronger
Weaker

Weaker
Volatile Chemicals
Chemicals that evaporate easily.
Nonvolatile Chemicals
Do not evaporate easily.
______________ temperatures cause higher evaporation rates.

High
Low

High
________________ surface areas cause higher evaporation rates.

Large
Small

Large.
Is vaporization endothermic or exothermic?
Endothermic
Is condensation endothermic or exothermic?
Exothermic
Enthalpy of Vaporization
The amount of heat required to vaporize 1 mole of liquid to a gas.
What is the Enthalpy of Vaporization for water?
ΔHvap = 40.7 kJ/mol
Dynamic Equilibrium
When the rate of a reverse process equals that of the forward process.

ex- when condensation = evaporization

Vapor Pressure
The pressure of a gas in dynamic equilibrium with it’s liquid.
Boiling Point
The temperature at which the liquid’s vapor pressure equals the external pressure.
Normal Boiling Pt.
The temperature of a liquid where its vapor pressure equals 1 atm.
Supercritical Fluid
Any substance beyond its critical point.
Critical Temperature (Tc)
The temp above which a liquid cannot exist regardless of pressure.
Critical Pressure (Pc)
The pressure required to bring about a transition to a liquid at Tc.
What properties do supercritical fluids hold?
Liquid and Gas
Sublimation
Solid to a gas
Deposition
Gas to a solid
What is an example of sublimation?
Dry Ice
Fusion
Melting; Solid to a liquid
Freezing
Liquid to a solid
Is fusion endothermic or exothermic?
Endothermic
Heat of Fusion
The amount of heat required to melt 1 mol of a solid.
Is freezing endothermic or exothermic?
Exothermic
Enthalpy of Sublimation
The amount of heat required to sublime 1 mol of a solid to a gas.
Phase Diagram
A map of the state(phase) of a substance as a function of pressure (y) and temperature (x).
Triple Point
Where all three states exist in equilibrium.
Critical Point
Represents the temp and pressure above which the supercritical point exists. Where a liquid and gas can no longer be distinguished.
Dipole-Dipole Forces
Exists between all molecules that are polar.
Permanent Dipole
When two atoms in a molecule have substantially different electronegativities.
Sometimes when we heat food in the microwave, the lid of the container pops off. Why does this occur?
The air and water vapor inside the container are expanding.
A substance with a fixed volume and fixed shape.
Solid
A substance with a fixed volume but no fixed shape.
Liquid
A substance with no fixed volume or shape.
Gas
What factors cause changes between the liquid and gas state?

A gas can be converted into a liquid by heating.

A gas can be converted into a liquid by cooling.

A liquid can be converted to a gas by heating.

A gas can be converted into a liquid by increasing the pressure of a gas sample.

A gas can be converted into a liquid by decreasing the pressure of a gas sample.

A liquid can be converted to a gas by cooling.

A gas can be converted into a liquid by cooling.

A liquid can be converted to a gas by heating.

A gas can be converted into a liquid by increasing the pressure of a gas sample.

What factors cause changes between the solid and liquid state?

A solid can be converted to a liquid by heating.

A liquid can be converted to a solid by cooling.

A liquid can be converted to a solid by heating.

A solid can be converted to a liquid by cooling.

A solid can be converted to a liquid by heating.

A liquid can be converted to a solid by cooling.

What are the main properties of liquids (in contrast to gases and solids)?

Liquids have a definite volume.

Liquids have much higher densities in comparison to gases.

Liquids have an indefinite shape and do not assume the shape of their container.

Liquids are easily compressed.

Liquids have an indefinite shape and assume the shape of their container.

Liquids are not easily compressed.

Liquids do not have a definite volume.

Liquids have lower densities in comparison to gases.

Liquids have a definite volume.

Liquids have much higher densities in comparison to gases.

Liquids have indefinite shape and assume the shape of their container.

Liquids are not easily compressed.

Which substance has the highest boiling point?

CH3OH

CO

N2

CH3OH
What are the correct conditions for forming a hydrogen bond?
A hydrogen atom acquires a partial positive charge when it is covalently bonded to an F atom.

Hydrogen bonding occurs when a hydrogen atom is covalently bonded to an N, O, or F atom.

A hydrogen bond is possible with only certain hydrogen-containing compounds.

The hydrides of group 5A are NH3, PH3, AsH3, and SbH3. Arrange them from highest to lowest boiling point.
SbH3, NH3, AsH3, SbH3.
Which molecules have dipole-dipole forces?

HF
CH3Cl
SiH4

HF and CH3Cl
How much energy is required to vaporize 135 g of butane at its boiling point? The heat of vaporization for butane is 23.1 kJ/mol.
53.7 kJ

(Molar mass and multiply)

What volume will 135 g of butane occupy at 745 torr and 35 ∘C?
59.9 L

(PV=nRT)

What happens to the vapor pressure of a substance when its surface area is increased at constant temperature?
The vapor pressure remains the same.
If hexane (C6H14), octane (C8H18), and octanol (C8H17OH) are heated evenly at different altitudes, rank them according to the order in which you would expect them to begin boiling.

Hexane at high altitude
Octane at sea level
Octanol at sea level
Octane at high altitude

Hexane at high altitude
Octane at high altitude
Octane at sea level
Octanol at sea level
Which of the following statements are correct?

When a solid is converted to a liquid, heat is absorbed.

The average kinetic energy of the system changes while all of a solid is converted to a liquid.

When heat is applied to a solid, the molecular motion decreases as the temperature increases.

Temperature remains constant while all of a solid is converted to a liquid.

The temperature increases while all of a liquid is converted to a gas.

When a solid is converted to a liquid, heat is absorbed.

Temperature remains constant while all of a solid is converted to a liquid.

When a small ice cube at -10∘C is put into a cup of water at room temperature, which of the following plays a greater role in cooling the liquid water: the warming of the ice from -10∘C to 0∘C , or the melting of the ice?
The melting of ice.
How much heat energy, in kilojoules, is required to convert 52.0 g of ice at −18.0 ∘C to water at 25.0 ∘C ?
24.8 kJ

Go through phase changes. Solid -> liquid calculations

How long would it take for 1.50 mol of water at 100.0 ∘C to be converted completely into steam if heat were added at a constant rate of 18.0 J/s ?
56.3 min

(Convert mol to g, multiply by deltaHvap, multiply by 18 J/s)

What is a phase diagram?
A phase diagram is simply a map of the phase of a substance as a function of pressure (on the y-axis) and temperature (on the x-axis)
What is the significance of crossing a line in a phase diagram?
It means that a phase transition has occurred.
The line connecting the triple point and the critical point on a phase diagram represents _____.

the temperature and pressure combinations above which only a supercritical fluid can exist

the temperature and pressure combinations at which the liquid and solid states are equally stable and at equilibrium

the temperature and pressure combinations at which the liquid and gas states are equally stable and at equilibrium

the temperature and pressure combinations at which the solid and gas states are equally stable and at equilibrium

the temperature and pressure combinations at which the liquid and gas states are equally stable and at equilibrium
Which intermolecular force correlates with dipole moment?
Dipole-Dipole Forces
Which intermolecular force correlates with polarizability?
Dispersion Forces
Carbon disulfide has a vapor pressure of 363 torr at 25∘C and a normal boiling point of 46.3∘C.

Find ΔHvap for carbon disulfide.

27 kJ/mol

Use Clausius-Clapeyron Equation

Methylamine has a vapor pressure of 344 torr at -25∘C and a boiling point of -6.4∘C .

Find ΔHvap for methylamine.

23 kJ/mol

Use Calusius-Clapeyron Equation

Explain why ice floats in water.
Ice is less dense than water.
Identify the state of matter that is the most compressible.
Gas
Identify the compound with the highest dipole moment.

CH3CHO
CH3CH2CH3
CH3OCH3
(CH3)2O
CH3CN

CH3CN
Identify the compound with the lowest boiling point.

(CH3)2O
CH3CH2CH3
CH3CN
CH3OCH3
CH3CHO

CH3CH2CH3
In DNA, adenine and thymine have ________ hydrogen bonds between them.
2
In DNA, cytosine and guanine hydrogen bond to each other with ________ hydrogen bonds.
3
The forces between polar molecules are known as
dipole-dipole forces
A molecule contains hydrogen bonding if it contains hydrogen covalently bonded to
F, O, and N.
A paper clip floating on the top of water is an example of
Surface Tension
For automobile engines, identify the best choice of motor oil.
Low SAE for Maine in the winter and high SAE for Florida in the summer.
Capillary action occurs because…
adhesive forces are greater than cohesive forces.
On a phase diagram, the sublimation curve is between
a solid and a gas.
On a phase diagram, the fusion curve is between
a solid and a liquid.
On a phase diagram, the vaporization curve is between
a liquid and a gas.
Define critical point.
The temperature and pressure above which a supercritical fluid exists.
Fresh vegetables with high water content do not freeze well. Explain.
Water expands when it freezes and damages the cell wall.
Which one of the following has a low density?

Liquid
Solid
Gas

Gas
Give the change in condition to go from a liquid to a gas.
Increase heat or reduce pressure.
Which is expected to have the largest dispersion forces?

F2
C9H20
SiH4
CH4

C9H20
Which of the following has the smallest dipole-dipole forces?

CO
F2
CH3CH2Cl
HI

F2
Choose the molecule or compound that exhibits dipole-dipole forces as its strongest intermolecular force.

BCl3
H2
CBr4
SO2
N2

SO2
Which of the following compounds exhibits dipole-dipole forces as its strongest attraction between molecules?

HBr
CO2
Kr
H2
CH3NH2

HBr
Identify the compound that does not have dipole-dipole forces as its strongest force.

CH3 I
HCBr3
CO2
CH2 Cl2
CH3OCH3

CO2
Which of the following compounds exhibits hydrogen bonding?

HCl
CH3OH
CH3Br
CH3SCH3

CH3OH
Choose the compound that exhibits hydrogen bonding as its strongest intermolecular force.

CH2Cl2
C2H6
CI4
CH3OH
None of the above compounds exhibit hydrogen bonding.

CH3OH
How many compounds, of the ones listed below, have hydrogen bonding?

CH3(CH2)2NH2

CH3(CH2)2NH(CH2)4CH3

(CH3CH2)2N(CH2)4CH3

2.
CH3(CH2)2NH2

CH3(CH2)2NH(CH2)4CH3

Identify the compound that does NOT have hydrogen bonding.

H2O
(CH3)2N(CH2)3CH3
CH3(CH2)2NH2
HF
CH3(CH2)5NH2

(CH3)2N(CH2)3CH3
What is the strongest type of intermolecular force present in CHCl3?
dipole-dipole
In liquid methanol,

CH3OH

which intermolecular forces are present?

Dispersion, dipole-dipole and hydrogen bonding.
Which halogen has the highest boiling point?

Br2
I2
Cl2

I2
Choose the substance with the highest surface tension.

CH3CH2CH2OH
CH3CH2CH2OH
CH3CH2I
CH2F2
HOCH2CH2OH

HOCH2CH2OH
Choose the substance with the lowest surface tension.

C6H6
CH3SeCH2CH3
(CH3)2SO
H2Se
CH3CH2CH2CH3

CH3CH2CH2CH3
Choose the substance with the highest viscosity.

C2H4Br2
(CH3CH2)2CO
HOCH2CH2CH2CH2OH
C8H18
CI4

HOCH2CH2CH2CH2OH
Choose the substance with the lowest viscosity.

SbBr3
AsBr5
SBr2
BeBr2
OBr2

BeBr2
Which of the following compounds has the highest boiling point?

H2S
H2Se
AsH3
H2O

H2O
Choose the substance with the highest vapor pressure at a given temperature.

SiS2
BH3
SbH3
RbBr
CH3OCH2CH3

BH3
Which of the following substances would you predict to have the highest ΔHvap?

CH3Cl
HOCH2CH2OH
CH3CH2OH
CH3CH2CH2CH3
HF

HOCH2CH2OH
The normal boiling point of water is ________ at sea level.
100 Celsius
How much energy is required to heat 36.0 g H2O from a liquid at 65°C to a gas at 115°C? The following physical data may be useful.

ΔHvap = 40.7 kJ/mol
Cliq = 4.18 J/g°/sup>C
Cgas = 2.01 J/g°/sup>C
Csol = 2.09 J/g°/sup>C
Tmelting = 0°/sup>C
Tboiling = 100°/sup>C

87.7 kJ
How much energy must be removed from a 125 g sample of benzene (molar mass= 78.11 g/mol) at 425.0 K to liquify the sample and lower the temperature to 335.0 K? The following physical data may be useful.

ΔHvap = 33.9 kJ/mol
ΔHfus = 9.8 kJ/mol
Cliq = 1.73 J/g°C
Cgas = 1.06 J/g°C
Csol = 1.51 J/g°C
Tmelting = 279.0 K
Tboiling = 353.0 K

67.7 kJ
How much energy is required to heat 87.1 g acetone (molar mass=58.08 g/mol) from a solid at -154.0°C to a liquid at -42.0°C? The following physical data may be useful.

ΔHfus = 7.27 kJ/mol
Cliq = 2.16 J/g°C
Cgas = 1.29 J/g°C
Csol = 1.65 J/g°C
Tmelting = -95.0°C

29.4 kJ
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