Unit 4: Liquids Flashcards
define intermolecular attractive forces
- exist between any two molecules
- some are stronger than others
are intermolecular forces generally stronger or weaker than chemical bonds
weaker
define miscibility
the property that describes two substances that will mix together (dissolve in one another)
which molecules are miscible and which are immisible
- miscible: polar and polar, nonpolar and nonpolar
- immiscible: polar and nonpolar
what is an easy way to remember miscibility rules
like dissolves like
define ion-dipole interactions
ionic solid dissolved in polar solvent
define dipole-dipole interactions
polar solute dissolved in polar solvent
what are the 4 types of dipole-dipole interactions
- 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)
what is the relationship between strength of polar bonds and strength on dipole-dipole interactions
more polar substances exhibit stronger dipole-dipole interactions
define hydrogen bonds
- 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
are hydrogen bonds strong or weak
unusually strong
are hydrogen bonds actual bonds
- no
- just interactions
explain why H makes hydrogen bonds when bonded with N, O, or F
- 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
explain how hydrogen bonds impact the density of ice
- 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
why are hydrogen bonds important in DNA
hold together the bases in DNA
define dispersion forces
weak electrostatic interactions between nonpolar compounds
what makes dispersion forces stronger
- larger polarizability
- larger atoms: strength increases with molecular weight
what is the strongest intermolecular force that can exist between nonpolar molecules
dispersion forces
what is the order of strength of intermolecular forces
- weakest: dispersion
- middle weakest: dipole-dipole
- strongest: ion-dipole and hydrogen bonds
what is the order of strength of intramolecular forces
- weakest: covalent bonds
- strongest: ionic bonds
which are stronger: intermolecular forces or intramolecular forces
intramolecular forces (within molecules)
describe the movement of particles in the gas phase
complete freedom of motion
describe the movement of particles in the liquid phase
free to move relative to each other
describe the movement of particles in the solid phase
particles in essentially foxed positions
do boiling points and melting points vary with pressure
- yes
- can be seen in a phase diagram
describe a phase diagram
shows the boiling and melting points of a substance based on temperature and pressure
at what pressure are the normal melting and boiling points of a substance
1 atm
define sublimation and deposition
- sublimation: transition of substance from solid state to gas state
- deposition: transition of substance from gas state to solid state
what is an example of a substance that undergoes sublimation and depostion
dry ice
what is the triple point in a phase diagram
the temperature and pressure where all 3 phases are in equillibrium
what is the critical point in a phase diagram
the temperature and pressure where you cannot distinguish between the liquid and gas phase
describe how the phase diagram of water differs from the phase diagrams of most other substances
- water: the line between the solid and liquid phase leans left
- other: the line between the solid and liquid phase leans right
what happens if you squeeze ice at a contsant temperature
it melts
why is the fact that the line between the solid and liquid phases in the phase diagram for water significant
explains why the liquid phase of water is more dense than the solid phase
in which phase of water are hydrogen bonds more stable
- more stable in ice
- less stable (constantly break and reform) in liquid
define vapor pressure
the pressure of molecules that evaporate all the time in any sample of liquid
describe the vapor pressure of volatile liquids
- vapor pressure is high
- causes the liquid to evaporate quickly
in which temperature range (high or low) do a higher proportion of molecules have the minimum kinetic energy needed to escape the liquid phase
higher temperature range
does vapor pressure vary with temperature
yes
do stronger or weaker intermolecular forces result in higher vapor pressure and why
- weaker intermolecular forces
- less force/energy required to break forces and get molecules into gas phase
why is the vapor pressure in volatile liquids high and how does this affect the boiling point
- molecules are experiencing weaker intermolecular forces
- have lower boiling points
what is the boiling point in terms of Pvap and Patm
the temperature where Pvap = Patm
do polar or nonpolar substances have a higher vapor pressure and why
- 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
do volatile liquids have a higher or lower boiling point than non-volatile liquids
lower
do compounds with stronger dispersion forces (larger) have higher or lower boiling points
higher boiling point
how do the boiling points of liquids at high altitudes (low pressure) compare to those at lower altitudes (high pressure)
lower boiling points at high altitudes
should you boil pasta for a longer or shorter amount of time at higher altitudes (low pressure)
longer time
