Unit 4: Liquids

Question 1

define intermolecular attractive forces

Answer 1

• exist between any two molecules
• some are stronger than others

Question 2

are intermolecular forces generally stronger or weaker than chemical bonds

Answer 2

weaker

Question 3

define miscibility

Answer 3

the property that describes two substances that will mix together (dissolve in one another)

Question 4

which molecules are miscible and which are immisible

Answer 4

• miscible: polar and polar, nonpolar and nonpolar
• immiscible: polar and nonpolar

Question 5

what is an easy way to remember miscibility rules

Answer 5

like dissolves like

Question 6

define ion-dipole interactions

Answer 6

ionic solid dissolved in polar solvent

Question 7

define dipole-dipole interactions

Answer 7

polar solute dissolved in polar solvent

Question 8

what are the 4 types of dipole-dipole interactions

Answer 8

• attraction on top of each other (double attraction)
• attraction from end to end (single attraction)
• repulsion on top of each other (double repulsion)
• repulsion from end to end (single repulsion)

Question 9

what is the relationship between strength of polar bonds and strength on dipole-dipole interactions

Answer 9

more polar substances exhibit stronger dipole-dipole interactions

Question 10

define hydrogen bonds

Answer 10

• dipole-dipole interactions when H is bonded with N, O, or F
• the H will interact with other atoms or molecules along with the N, O, or F that it’s bonded with

Question 11

are hydrogen bonds strong or weak

Answer 11

unusually strong

Question 12

are hydrogen bonds actual bonds

Answer 12

• no
• just interactions

Question 13

explain why H makes hydrogen bonds when bonded with N, O, or F

Answer 13

• N, O, and F are very electronegative so they pull electrons strongly to their side
• H become very positive and interacts with other atoms or molecules to satisfy electrons requirements

Question 14

explain how hydrogen bonds impact the density of ice

Answer 14

• hydrogen bonds in water when frozen create lots of holes in the structure, making ice less dense than water
• this allows the top layer of water to freeze and stay afloat while aquatic life continues underneath

Question 15

why are hydrogen bonds important in DNA

Answer 15

hold together the bases in DNA

Question 16

define dispersion forces

Answer 16

weak electrostatic interactions between nonpolar compounds

Question 17

what makes dispersion forces stronger

Answer 17

• larger polarizability
• larger atoms: strength increases with molecular weight

Question 18

what is the strongest intermolecular force that can exist between nonpolar molecules

Answer 18

dispersion forces

Question 19

what is the order of strength of intermolecular forces

Answer 19

• weakest: dispersion
• middle weakest: dipole-dipole
• strongest: ion-dipole and hydrogen bonds

Question 20

what is the order of strength of intramolecular forces

Answer 20

• weakest: covalent bonds
• strongest: ionic bonds

Question 21

which are stronger: intermolecular forces or intramolecular forces

Answer 21

intramolecular forces (within molecules)

Question 22

describe the movement of particles in the gas phase

Answer 22

complete freedom of motion

Question 23

describe the movement of particles in the liquid phase

Answer 23

free to move relative to each other

Question 24

describe the movement of particles in the solid phase

Answer 24

particles in essentially foxed positions

Question 25

do boiling points and melting points vary with pressure

Answer 25

- yes - can be seen in a phase diagram

Question 26

describe a phase diagram

Answer 26

shows the boiling and melting points of a substance based on temperature and pressure

Question 27

at what pressure are the normal melting and boiling points of a substance

Answer 27

1 atm

Question 28

define sublimation and deposition

Answer 28

- sublimation: transition of substance from solid state to gas state - deposition: transition of substance from gas state to solid state

Question 29

what is an example of a substance that undergoes sublimation and depostion

Answer 29

dry ice

Question 30

what is the triple point in a phase diagram

Answer 30

the temperature and pressure where all 3 phases are in equillibrium

Question 31

what is the critical point in a phase diagram

Answer 31

the temperature and pressure where you cannot distinguish between the liquid and gas phase

Question 32

describe how the phase diagram of water differs from the phase diagrams of most other substances

Answer 32

- water: the line between the solid and liquid phase leans left - other: the line between the solid and liquid phase leans right

Question 33

what happens if you squeeze ice at a contsant temperature

Answer 33

it melts

Question 34

why is the fact that the line between the solid and liquid phases in the phase diagram for water significant

Answer 34

explains why the liquid phase of water is more dense than the solid phase

Question 35

in which phase of water are hydrogen bonds more stable

Answer 35

- more stable in ice - less stable (constantly break and reform) in liquid

Question 36

define vapor pressure

Answer 36

the pressure of molecules that evaporate all the time in any sample of liquid

Question 37

describe the vapor pressure of volatile liquids

Answer 37

- vapor pressure is high - causes the liquid to evaporate quickly

Question 38

in which temperature range (high or low) do a higher proportion of molecules have the minimum kinetic energy needed to escape the liquid phase

Answer 38

higher temperature range

Question 39

does vapor pressure vary with temperature

Answer 39

yes

Question 40

do stronger or weaker intermolecular forces result in higher vapor pressure and why

Answer 40

- weaker intermolecular forces - less force/energy required to break forces and get molecules into gas phase

Question 41

why is the vapor pressure in volatile liquids high and how does this affect the boiling point

Answer 41

- molecules are experiencing weaker intermolecular forces - have lower boiling points

Question 42

what is the boiling point in terms of Pvap and Patm

Answer 42

the temperature where Pvap = Patm

Question 43

do polar or nonpolar substances have a higher vapor pressure and why

Answer 43

- nonpolar - nonpolar substances have weaker intermolecular forces (dispersion forces); easier for intermolecular forces to break which results in higher vapor pressure (meaning they are more volatile); also have a lower boiling point

Question 44

do volatile liquids have a higher or lower boiling point than non-volatile liquids

Answer 44

lower

Question 45

do compounds with stronger dispersion forces (larger) have higher or lower boiling points

Answer 45

higher boiling point

Question 46

how do the boiling points of liquids at high altitudes (low pressure) compare to those at lower altitudes (high pressure)

Answer 46

lower boiling points at high altitudes

Question 47

should you boil pasta for a longer or shorter amount of time at higher altitudes (low pressure)

Answer 47

longer time