Chapter 11: Liquids and intermolecular forces

Boiling Point

-higher pressure, higher boiling point -temperature at which its vapor pressure equals atmospheric pressure (external pressure) -normal boiling point is the boiling point at 760 torr (1 atm)

meniscuses (convex)

-if intermolecular forces are vastly different - adhesive < cohesive

adhesive forces

-intermolecular forces that bind a substance to a surface (capillary action)

cohesive forces

-intermolecular forces that bind similar molecules to each other (surface tension)

meniscuses (concave)

-liquid in a tube has a strong attraction to the molecules in the confined liquid - cohesive < adhesive

nonpolar solutes and polar solvents

-nonpolar compounds that do not interact at all with water will not mix with it

ion-dipole forces

-occur when an ionic compound is mixed with a polar compound -strongest of all

viscosity

-resistance of fluids to flow -larger the nonpolar chain, the stronger the viscosity -higher temperature, lower viscosity -london dispersion increases with surface area because more oppurtunity ot polarize & as strength increases, the viscosity increases

capillary action

-result of surface tension -arise because of a difference in intermolecular forces between a liquid and a surface

heating curve

-shows how a substance's temperature changes as heat is added

cooling curve

-shows how a substance's temperature changes as heat is removed

Polar solutes and polar solvents

-small neutral molecules with O or N atoms that can hydrogen bond to water are water soluable

what would have the least interaction with a Li_+ ion

-smaller size of the Li+ means that ion-dipole interactions with polar molecules are stronger. So, nonpolar molecules would have a weaker attraction

Surface tension

-stronger the forces, the stronger the surface tension -results from the net inward force experienced by molecule on the surface of a liquid

heat of vaporization

-the amount of heat needed to vaporize a liquid -used to calculate the amount of energy required to vaporize a given mass of that liquid -opposite is the heat of condensation

identify a factor that affects the boiling point of a pure substance

-vapor pressure -intermolecular forces' strength -enthalpy of vaporization

london dispersion forces

-very weak interactions due to the momentary changes in electron density in a molecule -creates a temporary dipole -ALL COVALENT BONDS exhibit london dispersion forces

effects of intermolecular forces

1. surface tension 2. viscosity 3. capillary action

triple point

3 phases present in equilibrium

which alkane compound has the highest vapor pressure? a. C4H10 b. C5H12 c. C6H14 d. C7H16 e. C8H18

a. (smallest surface area- weaker dispersion forces - higher vapor pressure)

ion-dipole forces always require______

an ion and a polar molecule

Larger the molecule, larger the _______

attractive force and the intermolecular force -as the number of electrons increase (larger molar mass), the dispersion forces increase, and so does the boiling point

intermolecular forces between molecules are due to ______

attractive forces between opposite charges -permanent charges as ions or dipoles -temporary charges (polarizability) can be induced or spontaneous

Water forms a concave meniscus in a glass tube because ________ a the cohesive forces between water molecules are larger than the adhesive forces between water molecules and the glass wall. b the adhesive forces between water molecules and the glass wall are larger than the cohesive forces between water molecules. c water molecules form hydrogen bonds with each other. d water molecules repel each other. e the glass wall is wet.

b

Which molecule has the largest dipole? a. CH4 b. NH3 c. SO3 d. CO2 eC2H4

b. (highest polarity)

Which of the following polar compounds is likely to have the highest boiling point? a. CH3OCH3 b. CH3CH2OH c. (CH3)2CO d. H2CO e. CO

b. (hydrogen bond - larger forces- higher boiling point)

Which best describes the intermolecular forces present in NH3 a. only dispersion b. hydrogen bonding and dispersion c. dipole-dipole, hydrogen bonding, and dispersion d. dipole-dipole only e. ion dipole and dispersion

c

Which of the following solvents will involve ion dipole interactions with Na+? a benzene (C6H6) b carbon tetrachloride (CCl4) c chloroform (CHCl3) d cyclohexane (C6H12) e pentane (C5H12)

c

Based on their boiling points, which of the following compounds has the largest dipole dipole interaction? a propane (231 K) b dimethyl ether (248 K) c acetonitrile (355 K) d methyl chloride (249 K) e butane (135 K)

c (higher the boiling point, the higher the intermolecular forces)

Which of the following nonpolar molecules will have the highest boiling point? a. CO2 b. C6H6 c. C6F6 d. C2H2 e. CF4

c. (larger surface area (flourine > hydrogen in size) - stronger the dispersion forces - higher the boiling point)

Which of the following compounds is capable of dipole-dipole interactions? a. Ch4 b. CO2 c. H2CO d. SF6 e. NH4

c. (only polar compound)

At the critical point, ________ a all the liquid has evaporated. b the densities of the solid and the liquid are the same. c the densities of the solid and the gas are the same. d the densities of the gas and the liquid are the same. e a critical mass has been reached.

d

Normal boiling points of branched alkane hydrocarbons generally are lower than for straight-chain hydrocarbons of the same molar mass because the straight-chain hydrocarbons ________ a have stronger dipole dipole interactions. b have many more electrons. c have more C H bonds. d have a larger surface area and come in closer contact with each other. e react with each other to form long chains.

d

Which of the following compounds will have the strongest dipole dipole interactions between its molecules? a.CF4 b.CH4 c.CH3F d.CH2F2 e.CH3Cl

d (largest molecule with the strongest electronegativity)

Which alcohol should be most soluble in a polar solvent such as hexane, C6H14 a. CH3OH b. CH3CH2OH c. CH3CH2CH2OH d. Ch3CH2CH2CH2OH e. CH3CH2CH2CH2CH2OH

e (has a much larger nonpolar section than polar)

Which of the following compounds do you expect to be most soluble in water? a. CO2 b. CCl4 c. O2 d. SiO2 e. NH3

e (highest polarity)

Which of the following molecules exhibits the greatest london dispersion forces? a. CH3CH3 b. CH3CH2CH3 c. C2H2 d. CH4 e. CH3CH2CH2CH3

e (largest surface area)

Which alkane compound has the highest boiling point? a. C4H10 b. C5H12 c. C6H14 d. C7H16 e. C8H18

e (largest surface area- larger dispersoin forces)

which alkane compound has the lowest vapor pressure? a. C4H10 b. C5H12 c. C6H14 d. C7H16 e. C8H18

e. (larger surface area- stronger dispersion forces- lower vapor pressure)

Which of the following compounds would be most soluble in water? a.CH4 b.H2 c.N2 d.C2H4 e.CH3OH

e. (only polar molecule)

for a molecule to exhibit dipole-dipole interactions it must______

have a permanent dipole

boiling point _____ with the stronger the dipole-dipole

increases

_____ the dispersion force, the ______ the molecule with covalent bonds

larger, larger

strength of intermolecular forces determine whether a compound has a high or low______

melting and boiling points

During a phase change temperature __________

remains constant

intermolecular forces are not nearly as ________ as intramolecular attractions

strong but strong enough to control boiling, melting, pressures & viscositites

dipole-dipole are not as ______ as ion-dipole because_____

strong; dipole-dipole interactions only involve partial charges by unequal sharing of electrons

dispersion forces are due to

temporary dipoles

why is shape important?

the larger the surface area, more electrons have a higher chance of becoming polarized which increases the boiling point and london dispersion forces

the vapor pressure of a liquid will increase if ____

the temperature increases

miscibility of solvents

whether or not liquids are miscible is affected by the intermolecular forces

the critical point

-above a certain temperature, liquids cease to exist as a separate phase -critical temperature (pressure and volume) -usually only temp and pressure are tabulated because the critical volume is hard to measure and not needed

Dispersion forces

-an instantaneous dipole on any one atom induces instantaneous dipoles on a neighboring atom -larger the size of the atom, the larger the dispersion force

dipole-dipole interactions

-attractive forces between the permanent dipoles of two polar molecules - higher the polarity the higher the boiling point

unusual features of CO2

-cannot exist in liquid phase at pressures below 5.1 atm (tripple point)

nonpolar solutes and nonpolar solvents

-exhibit london dispersion forces -nonpolar compounds are soluble in nonpolar solvents

hydration sphere

-forms around an ion in aqueous solution due to ion-dipole interactions

fusion or melting

-heat absorbed upon melting ot the heat given off upon freezing -melting: endothermic -freezing: exothermic

hydrogen bonds

F,O,N -highest boiling point, melting point, and strength

sublimation and deposition

Hsub = Hfus + Hvap Hdep = -Hsub

Which of the following statements does not correctly identify a factor that affects the boiling point of a pure substance? I. vapor pressure of the liquid II. strength of intermolecular forces III. enthalpy of vaporization IV. surface area of the liquid

IV only

Arrange the following compounds in order of increasing dispersion interactions: CCl4, CH4, C3H8. a CH4 < C3H8 < CCl4 b CCl4 < CH4 < C3H8 c C3H8 < CH4 < CCl4 d CCl4 < C3H8 < CH4 e CH4 < CCl4 < C3H8

a

For molecules, atoms, or ions with the same mass, which of the following force typically is the strongest intermolecular interaction? a ion dipole b hydrogen bonding c dipole dipole d dispersion e ion-induced dipole

a

Polarizability refers to ________ A the ease with which the electron cloud of an atom or molecule can be distorted. B the magnitude of the dipole moment of a molecule. C the ease with which a hydrogen bond can form. D the perturbation in electron density because of hydrogen bonding. E the ability to transmit polarized light.

a

Which is the dominant interaction that explains the high melting point of table salt, NaCl? a ion ion b ion dipole c dipole dipole d hydrogen bonding e dispersion or London forces

a

Which of the following compounds would you most appropriately call hydrophobic? a CH4 b H2CO c CO d HCl e NaCl

a (aka nonpolar)