Midterm 2 - Solids, Liquids, and IMFs

gas properties

low density, shape of container, volume of container

* can be compressed (boyle’s law)

liquid properties

high density, shape of container, volume is definite

* cannot be compressed

solid properties

high density, definite shape, and definite volume

* cannot be compressed

melting

solid → liquid

* take in energy (endothermic)

freezing

liquid → solid

* releases heat energy (exothermic)

boiling/evaporating

liquid → gas

* endothermic
* involves the heat of vaporization

condensing

gas → liquid

* exothermic

freezing

liquid → solid

* exothermic

sublimation

solid → gas

* endothermic
* ex - dry ice

deposition

gas → solid

* exothermic

does a change in state change the chemical composition?

no, it is only a physical change, not a chemical change

intermolecular forces (IMFs)

forces that occur between molecules

* arise from differences in charges within molecules

IMFs - weakest to strongest

london dispersion forces, dipole-dipole, hydrogen bonding, ion-dipole forces, metallic bonding

dipole-dipole IMFs

in molecules with a dipole (polar)

* + end attracts -
* transient interaction
* larger the dipole of a molecule = stronger the dipole-dipole forces
* if the VSEPR has lone electrons on center, probably polar

temperature and strength of dipole-dipole

higher boiling point = higher melting point = stronger dipole (directly proportional)

ion-dipole forces

dipole-dipole, except one is an ion

hydrogen bonding

H bonded to N, O, or F between molecules

* large difference in electronegativity = larger partial charge
* transient interaction
* more H bond donors and acceptirs = high the difference in properties

H-bond donor

provides the H+ that bonds with the negatively charged ion

H-bond acceptor

the negatively charged atom that is receiving the H+ bond (O, N, F)

are polar compounds acceptors or donors

only acceptors

are OH, NH, and FH donors or acceptors

both donors and acceptors

is H2O a donor or acceptor

both because it is polar (acceptor) and has an OH on both sides (donor)

* molecules with NOF not attached to H can form h-bonds with H2O

h-bonding in DNA

interactions between base pairs are H-bonds

* IMFs allows the bonds to zip and unzip

h-bonding in amino acids

hold together amino acids

h-bonds in plant structure

form h-bonds with hydrozyl groups in cellulose and makes strong structure

london dispersion forces (LDFs)

caused by instantaneous uneven distruction of electron density within an atom or molecule (instant dipole)

* in all atoms/molecules
* small amount of attraction

LDFs and electrons

more electrons = larger polarizable e- cloud = stronger LDF (polarizability)

* larger molecular weight = larger forces (atomic #)

h-bond donors/acceptors and temperature

more H+ bond donors and acceptors = higher boiling and melting points

rate increases with

increasing temp, surface area, and decreasing IMFs

heat of vaporization

energy required to vaporize one mole of a species

* overcome intermolecular forces
* endothermic
* heat released during condensation is the same but opposite sign (-)
* required for vaporization

heat of fusion

the heat released when something freezes is equal in magnitude, opposite in sign

* required for melting

water and its exception

* low molar mass
* strong dipole/ h-bonds
* high melting and boiling points
* high polarity (dissolves polar and ionic species)
* high heat capacity

surface tension

liquids tend to attract each other, minimizing surface area

* higher IMF = higher surface tension
* less molecules to interact with on surface

viscosity

resistance fo liquid to flow

* lower temp = higher viscosity
* higher IMF = higher viscosity

capillary action

the ability of a liquid to flow against gravity in a narrow tube

* higher adhesive forces = lower cohesive forces = more capillary action

cohesive forces

attraction between molecules in a liquid

adhesive forces

attraction between molecules in a liquid and the walls of the tube

vapor pressure

the partial pressure that the vaporized liquid can exert in thermodynamic equilibrium with its liquid or solid forms

relationship of IMFs, molecules, and vapor pressure

weak IMFs = more molecules in the gas phase = higher vapor pressure

how much liquid is present in a container?

1. plug in given into n = PV/rT to find the mols of gas that the space can hold
2. convert to grams (if liquid is given in g)
3. subtract the found from the given amount of liquid to find the liquid leftover

heating curve

1. solid - increasing until melting point (q=mC△T)
2. solid → liquid - constant T (q = △H(fus) n)
3. liquid - increasing to boiling point
4. liquid → gas - constant T (q = △H(vap) n)
5. gas - rising T (q=mC△T)

\
C = specific heat capacity for phase

△T = final - initial

m = given