Chapter 11 Intermolecular Forces and the Liquid State

Question 1

Fusion (Melting)

Answer 1

solid to liquid; endothermic

Question 2

Vaporization

Answer 2

liquid to gas; endothermic

Question 3

Sublimation

Answer 3

solid to gas; endothermic

Question 4

Freezing

Answer 4

liquid to solid; exothermic

Question 5

Condensation

Answer 5

gas to liquid; exothermic

Question 6

Deposition

Answer 6

gas to solid; exothermic

Question 7

Enthalpy of Vaporization

Answer 7

energy required to convert 1 mole or 1 gram of a liquid to vapor at a given temperature

Question 8

When the strength of the IMFs in a series of liquids increase, will the enthalpy of vaporization increase or decrease?

Answer 8

increase because it will require more energy to break the bonds

Question 9

Dynamic Equilibrium

Answer 9

state in which the rates of vaporization and condensation are equal

Question 10

What happens to temperature when vapor pressure increases?

Answer 10

as temperature increases, vapor pressure increases too

Question 11

When the strength of the IMFs in a series of liquids increase, will the vapor pressure increase or decrease?

Answer 11

decrease because molecules with weaker IMFs are held less tightly to one another in the liquid phase so more of them can escape into the vapor phase

Question 12

Surface Force

Answer 12

measure of force required to break the surface of the liquid

Question 13

Do liquids with strong IMFs have high or low surface tension?

Answer 13

high surface tension

Question 14

Viscosity

Answer 14

measure of a liquid’s resistance to flow

Question 15

What does viscosity depend on?

Answer 15

IMF strength and length of the molecules in the liquid

Question 16

Capillary Action

Answer 16

the result of the cohesive forces within a bulk sample of a liquid being overcome by adhesive forces

Question 17

Dipole-dipole IMF

Answer 17

attractive forces that occur between two polar molecules

Question 18

What do polar molecules have?

Answer 18

a permanent dipole; there is a partial positive charge at one end and a partial negative charge at the other end

Question 19

Hydrogen Bonding

Answer 19

strong type of dipole-dipole IMF that occurs between NOF

Question 20

Why are hydrogen bonds so strong?

Answer 20

1. the elements bonded to H are very electronegative whereas H has a low electronegativity, resulting in a ver polar bonds
2. H has a very small size, allowing hydrogen-bonding molecules to approach very closely and the smaller distance results in a stronger force of attraction

Question 21

Which is stronger? Hydrogen bonds or dipole-dipole IMFs?

Answer 21

hydrogen bonds

Question 22

Dipole-Induced Dipole Forces

Answer 22

attractive forces that occur between polar and nonpolar molecules; nonpolar molecules do not have permanent dipoles but it is possible to induce a temporary dipole in a nonpolar molecule

Question 23

Are dipole-dipole forces always stronger than dipole-induced dipole forces?

Answer 23

not always because the magnitude of the dipole-induced dipole can result in a force stronger than dipole-dipole forces

Question 24

Polarizibility

Answer 24

the extent to which the electron cloud of an atom or molecule can be distorted by an external electric charge

Question 25

As the number of electrons in a molecule increase, does the polarizibility increase or decrease?

Answer 25

it increases; therefore, it increases with increasing molar mass and molecular size

Question 26

Induced Dipole-Induced Dipole Forces/London Dispersion Forces/Dispersion Forces

Answer 26

attractive forces that occur between nonpolar molecules; there is no preferred directionality

Question 27

Are dispersion forces always weaker than dipole-dipole forces?

Answer 27

no, they can be stronger than dipole-dipole forces when they occur between highly polarizable molecules

Question 28

Dispersion forces are important in all liquids, even those consisting of polar molecules, why?

Answer 28

because any electron cloud can be distorted by the partial changes in surrounding molecules

Question 29

What happens to the boiling point as molar mass decreases?

Answer 29

boiling point decreases too

Question 30

Are Group 6A hydrides polar or nonpolar?

Answer 30

polar; therefore, there are dipole-dipole IMFs in pure liquids

Question 31

Why is the boiling point for water so high?

Answer 31

because there is extensive hydrogen bonding in water

Question 32

Besides high boiling point, what other properties do hydrogen bonds in water molecules influence?

Answer 32

1. high enthalpy of vaporization
2. high surface tension
3. high heat capacity