Chapter 11: Liquids, Solids, and Intermolecular Forces

Question 1

Coulomb’s law

Answer 1

Potential energy (E) and distance (r) are inversely related

E decreases (becomes more negative) as r decreases

Potential energy and product of charges are directly related

E decreases as q₁q₂ decreases (becomes more negative)

*q₁ and q₂ are of opposite signs (charges)

Question 2

Effect of intermolecular forces on boiling and melting points

Answer 2

High intermolecular forces = high boiling/melting point

Question 3

Dispersion force

Answer 3

Result of fluctuations in the electron distribution within molecules or atoms

Depends on fleeting charge separation called instantaneous or temporary dipole

Stronger dispersion force:
Higher molar mass (polarizability)
More surface area (longer chains)

Question 4

Instantaneous/temporary dipole

Answer 4

Associated with dispersion force

When an atom or molecule displays polarity temporarily (as electrons are constantly moving and bond to be dense on one end)

Question 5

Permanent dipole

Answer 5

Characteristic of a polar molecule where positive and negative ends can interact with opposite ends of other like molecules

Associated with dipole-dipole force

Question 6

Miscibility

Answer 6

Ability to mix without separting into two states

“Like dissolves like”

*Oil and water are immiscible

Question 7

Hydrogen bond

Answer 7

Occurs when N, O, or F are bonded directly to a hydrogen

Special kind of dipole-dipole force where H has the partial positive charge and F, O, or N has the partial negative charge

Question 8

Ion-dipole forces

Answer 8

Present only in mixtures of substances (ionic + polar)

Question 9

Strengths of intermolecular forces

Answer 9

Dispersion < Dipole-dipole < H-bonding < Ion-dipole

Question 10

Surface tension

Answer 10

Energy required to increase the surface area of a liquid by a unit amount

Molecules on surface are strongly attracted by interior molecules

Higher surface tension = greater intermolecular forces

Temperature increases –> surface tension decreases

Question 11

Viscosity

Answer 11

Liquid’s resistance to flow

Higher viscosity = stronger intermolecular forces

More spherical molecules = less viscous
(Chains are more viscous)

Temperature increases –> viscosity decreases

Question 12

Capillary action

Answer 12

The ability of a liquid to flow (“climb” up a thin tube against influence of gravity

Depends on two forces:
Cohesion
Adhesion

The stronger the cohesion (intermolecular forces), the smaller the capillary action

Question 13

Cohesive forces

Answer 13

Forces that hold liquid molecules together

Question 14

Adhesive forces

Answer 14

Forces that attract the outer liquid molecules to tube’s surface

Question 15

Vaporization

Answer 15

AKA evaporation

Escape of molecules from liquid to gas phase - endothermic

Kinetic energies vary within liquid body

Molecules on surface have higher kinetic energies and more easily overcome intermolecular forces

Affected by:
Temperature
Surface area
Intermolecular forces (volatility)

Question 16

Condensation

Answer 16

Molecules transition from gas to liquid phase - exothermic

Some molecules lose energy through collisions and liquid [re]captures them

Question 17

Dynamic equilibrium

Answer 17

Occurs when two opposite processes reach the same rate so that there is no net gain or loss of material

Rate of evaporation = constant
Rate of condensation = increases until met with rate of evap

Question 18

Vapor pressure

Answer 18

Pressure exerted by a vapor when it is in dynamic equilibrium with its liquid

Quantity & surface area = negligible

Vapor pressure increases with temperature and with decreasing strength of intermolecular forces

Question 19

Heat (enthalpy of vaporation)

Answer 19

ΔH_vap = -ΔH_condensation

The amount of heat energy required to vaporize one mole of a liquid

kJ/mol

Somewhat temperature dependent

Question 20

Boiling point

Answer 20

Temperature at which vapor pressure of liquid is = to external pressure above liquid

Question 21

Normal boiling point

Answer 21

Temperature at which the vapor pressure of a liquid equals 1 atm

Question 22

The Clausius-Clapeyron Equation

Answer 22

ln P₂/P₁ = (-ΔH_vap/R) (1/T₂-T₁)

R = 8.314 J/mol K

T = in Kelvin

Question 23

Supercritical fluid

Answer 23

Properties are intermediate between a liquid and gas

Occurs at critical temperature and pressure

Question 24

Sublimation

Answer 24

Phase transition solid to gas - endothermic

Question 25

Deposition

Answer 25

Phase transition from gas to solid - exothermic

Question 26

Fusion

Answer 26

AKA melting

Phase transition from solid to liquid - endothermic

Question 27

Freezing

Answer 27

Phase transition from liquid to solid - exothermic

Question 28

Heat (enthalpy) of fusion

Answer 28

ΔH_fus = -ΔH_{crystallization}

Somewhat temperature dependent

The amount of heat energy required to melt one mole of a solid (kJ/mol)

Question 29

Uniqueness of water

Answer 29

Liquid at room temperature (despite low molar mass)

Excellent solvent for polar & ionic compounds

Very high specific heat capacity

Expands when it freezes (unusual)
(Solid less dense than liquid – also unusual)

(Because of strong hydrogen bonds)

Question 30

Equation for heat involved in completion of a phase change

Answer 30

q = nΔH_transition

heat = # of mols * heat of [transition]

Question 31

Equation for heat involved in temperature change

Answer 31

q = (m) (C_s) (ΔT)