Phases And Phase Changes

Front 1

3 unit cells for lattice structures

Back 1

1) simple cubic, 1 atom
2) body centered cubic, 2 atoms
3) face centered, 4 atoms

Front 2

why do liquids have highest heat capacity?
colligative property (heat capacity)

Back 2

they can absorb energy in rotational, vibrational, and translation forms

heat capacity increases with solute, -extra energy that would go towards increasing avg. speed is directed towards weakening intermolecular attractions

Front 3

liquid water density

Back 3

density decreases and volume increases with increasing temperature
most dense form is at 4 ºC

Front 4

triple point

Back 4

gas, liquid, and solid coexist at this pressure and temperature

Front 5

critical point

Back 5

highest temp and pressure a liquid can exist at, beyond which liquid and gas are indistinguishable.

*clumps of molecules fill the volume of a container with density highest at the bottom

Front 6

fusion, vaporization, and sublimation
-define
-compare enthalpy
(explain)

Back 6

fusion: liquid→←solid
vaporization: liquid →←gas
sublimation: solid →←gas

enthalpy is greatest for sublimation and least for fusion. it takes more energy to weaken intermolecular bonds than to weaken them

Front 7

platues and slopes of a heating curve

Back 7

platues are phase changes where additional heat goes towards breaking/weakening intermolecular forces instead of increasing avg speed of molecule (temperature doesn't change)

slopes can be used to determine heat capacity (calorie / gram*Kelvin)

Front 8

atypical water phase diagram

Back 8

the solid/liquid line has a negative slope.
*in isothemal conditions, an increase of pressure will turn solid to liquid (densest form for water)

*phase diagram only shows most likely phase

Front 9

raoult's law

Back 9

for miscible liquids,
vapor pressure = (mol fraction)(vapor pressure of pure liquid)

*that's the percent of liquid that is exposed for evaporation
*volatile liquids have higher mol fraction in vapor than in solution

Front 10

vapor pressure determinants

Back 10

1)▲H vap: energy needed to overcome intermolecular forces
-MW
-polarity/H-bonding
2)temperature

NOT dependent on exposed surface area (units are force per area)
OR external pressure

Front 11

clausius clapeyron

Back 11

exponential relationship between vapor pressure and temperature
*think sudden boiling of water
ln (P1) - ln (P2) =
(▲Hvap /R) (1/T1 -1/T2)

▲Hvap is always positive because evaporation is endothermic

Front 12

boiling point and vapor pressure

Back 12

when vapor pressure equals atmospheric pressure, the liquid boils. 760 torr for 1 atm

you can alter boiling temp by changing atm pressure

Front 13

-volatility of solutions
-solution boiling point
-deviations from Raoult's Law
(G,H, S)

Back 13

daltons law of partial pressure, add the partial pressures from Raoult's law, when the combined vapor pressure equals atm pressure it will boil
*adding a volatile liquid will decrease boiling point

raoults law and daltons partial pressure would predict a linear relation between mol fraction of two liquids and boiling point

Front 14

freezing point depression reasoning

Back 14

attractions between ions and water are stronger than dipole-dipole (H-bonding) water attractions.

these attractions only exist in solution form so there is a pull in that direction

water/ion attractions are exothermic

effects are exaggerated as water freezes and concentration of water/ion solution is higher

Front 15

boiling point elevation explanation

Back 15

*is equivalent to decreasing vapor pressure

attractions between ions and water are stronger than h-bonding water attractions because an ion's positive charge is larger than the partial positive charge on the hydrogen of water

attractions only exist in solution (liquid form)

less surface area is exposed for evaporation

more energy is needed to weaken intermolecular attractions that could have gone to raising avg KE

*heat capacity increases

Front 16

calculating elevated bp and reduced mp

Back 16

▲Tb = Kb*i*m
▲Tf = Kf*i*m

-m is molality (mols/kg solvent)
-i is vant' hoff factor (# of ions that form from disassociation)
(sugar = 1, MgCl2 = 3)

Front 17

osmotic pressure
-define/equation
-U-tube

Back 17

pressure needed to stop the flow of water through a semi-permeable membrane as it travels from low to high concentration of solute

in a u-tube, water will stop flowing when osmotic pressure is equal to hydrostatic force

(density*g*▲h) = M*i*R*T

M is molarity, T is in Kelvin

Front 18

condosity

Back 18

molecularity of NaCl required to produce equal specific conductance

if condosity is greater than molarity, the salt is a better conductor than NaCl

a large ratio of condosity to molarity indicates an effectively conducting ion

Front 19

water h-bonding

Back 19

is stronger than other similar H-bonding molecules so it has a higher bp

Front 20

adiabatic

Back 20

no heat exchange

Front 21

amorphous

Back 21

no shape

Front 22

rate of vapor pressure in a solution

Back 22

it will decrease as the percent of the more volatile liquid decreases

Front 23

energy needed to heat a substance from liquid phase through gas phase

Back 23

heat capacity (liquid) * ▲T * grams
+ Hvap
+ heat capacity (gas) * ▲T * grams

Front 24

vapor density

Back 24

since gas all have equivalent molar volume, density is determined by MW

Front 25

-deviations from raoult's law
-solvation (dilution) ▲H,▲S,▲G

Back 25

deviations occur when
1) intermolecular attractions between the two solutes lower the expected vapor pressure ( -▲G, -▲H, +▲S)
2) repulsion raises expected pressure
(-▲G, +▲H, +▲S)

*there is -▲G (exergonic)if it dissolves spontaneously
*deviations are small unless a chemical reaction takes place

Front 26

distillation

Back 26

solution will be partially vaporized repeatedly, the vapor collected through condensation. each subsequent evaporation increases the % of the more volatile vapor.
(fractional distillation vs. simple)
entropy decreases, (-)▲S

Front 27

allotrope

Back 27

same element, different bonds, different MW, different molecular properties