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CHEM 1212: Exam 1
The forces holding solids and liquids together |
intermolecular forces |
intermolecular forces are a function of: |
1 - charge
2 - polarity
3 - molar mass |
What are the four important intermolecular forces and rank them from strongest to weakest |
1 - ion ion interactions
2 - hydrogen bonding
3 - dipole dipole
4 - Dispersion forces |
The force of attraction between two oppositely charged ions is governed by |
Coulomb's law |
In terms of intermolecular forces, greater charge = _____ |
stronger attraction |
In terms of intermolecular forces, greater distance = ___ |
weaker attraction |
Coulomb's law determines what two things? |
1 - the melting and boiling points of ionic compounds
2 - the solubility of ionic compounds |
dipole dipole interactions become less important as _____ |
temperature increases |
dipole dipole compounds are more volatile than ionic compounds because _____ |
they are held less tightly |
Strong H-bonding occurs among ______ |
polar covalent molecules containting H bonded to either F, O, or N |
The molecule that has an H attached to either F, 0, or N |
hydrogen bond donor |
the molecule that has an F, O, or N |
hydrogen bond acceptor |
What forces are present between all types of molecules |
london dispersion forces |
Dispersion forces are stronger for molecules with ______ |
more electrons or that are larger |
Dispersion forces are caused by ____ |
the polarization of the e- cloud of an atom or molecule |
Polarizability increases with increasing ____ |
number of e- and therefore with increasing sizes of molecules |
London dispersion forces are a function of ______ |
molecular polarizibility |
5 properties of a liquid |
particles are in constant motion
- particles are in close contact
- liquids are almost incompressible
- liquids do not fill the container
- intermolecular forces are relevant
|
process in which a substance in the liquid state becomes a gas |
Vaporization or condensation |
Vaporization is dependent on _____ |
temperature |
describe the idea of "cooling by evaporation" |
only the higher energy molecules can evaporate from the liquid. so then the liquid cools because the high energy hot ones have left |
When molecules of liquid are in the vapor state, they exert a ______ |
vapor pressure |
____ is the pressure exerted by a vapor over a liquid in a closed container |
equilibrium vapor pressure |
At equilibrium, rate of evaporation = _____ |
rate of condensation |
The vapor pressure of a liquid is seen to _____ with temperature |
increase exponentially |
The rate of evaporation equals the rate of condensation in a closed container |
dynamic equilibrium |
The vapor pressure of a liquid is a measure of the _______ |
tendency of its molecules to escape from the liquid phase and enter the vapor phase at given T |
Vapor pressure of liquids always increase as _____ |
temp increases |
liquids that are easily vaporized and have relatively high vapor pressures |
volatile liquids |
What do stronger attractive forces do for vapor pressure? |
lower it |
As long as some liquid remains in contact with the vapor, the vapor pressure does not depend on ____ |
volume or surface area |
Three things the Clausius-Clapeyron equation is used for |
- predict the vapor P of liquid at new T
- determine what T we must heat something to get specific vapor P
- calculate delta H if we know |
What is the Clausius-Clapeyron Equation? |
ln (P2/P1) ≈ (ΔHvap / 8.314 J mol-1 K-1) (1/T1 - 1/T2)
The equation relates the vapor pressure of a substance at 2 different temperatures as a function of its enthalpy of vaporization.
It can also relate the vapor pressures over a solid in terms of the enthalpy of sublimation. |
Temperature at which a liquids vapor pressure is equal to the external pressure |
boiling point |
What is the critical point? |
point at which a high enough temp and pressure has been reached so that the interface between liquid and gas disappears |
Temperature above which a gas cannot be liquefied |
critical temp |
the pressure required to liquefy a gas at its critical temp |
critical pressure |
the combination of critical T and critical P |
critical point |
A substance at a temperature above its critical temperature |
supercritical fluid |
a measure of the unequal attractions that occur at the surface of a liquid or a measure of inward forces that must be overcome to expand the surface area of a liquid
|
surface tension |
the ability of a liquid to rise or fall in a glass tube or other container |
capillary action |
forces that hold liquids together |
cohesive forces |
forces between a liquid and a solid surface |
adhesive forces |
the resistance to flow in a liquid |
viscosity |
Viscosity ___ with increasing T |
decreases |
noncrystalline solids, have no well-defined, ordered structure |
amorphous solids |
have well defined structure and sharp melting temperatures |
crystalline solids |
4 properties of solids |
1 - molecules, atoms, or ions locked into crystal lattice
2 - particles are close together
3 - exhibit strong intermolecular forces
4 - highly ordered, rigid, incompressible |
the smallest repeating internal unit that has the symmetry characteristics of the solid |
unit cell |
2 reasons why unit cells are important |
1 - a number of metals, ionic solids, and intermetallic compounds crystallize in cubic unit cells
2 - it's relatively easy to do calculations with these unit cells |
3 variations of the cubic crystal system |
- Simple or primitive
- body centered
- face centered |
how many particles are in each of the three unit cells? |
Simple - 1
BCC - 2
FCC - 4 |
Radius equation for simple cubic |
r = a/2 |
radius equation for body centered |
r = [(a)sqrt(3)]/4 |
radius equation for face centered |
r = [(a)sqrt(2)]/4 |
have ions that occupy the positions in the unit cell |
ionic solids |
____ was introduced to rationalize covalent bonding in molecules and can also be used to describe metallic bonding |
molecular orbital theory |
Idea that the electrons are associated with all the atoms in the crystal and not with specific bonded atoms |
delocalized |
a barrier to the promotion of electrons to a higher energy level |
Band gap |
naturally occurring property of the pure metal |
intrinsic semiconductors |
conductivity of material is changed by adding/doping the material with a different element |
extrinsic semiconductors |
Why do ionic compounds have high melting points? |
because ion ion interactions are so strong |
The lattice energy of a salt is dependent upon _____ |
charge and size of the ions |
The energy released when a mole of formula units of a solid is formed from its constituent ions in the gas phase |
crystal lattice energy |
The crystal lattice energy is a measure of the ____ |
attractive forces in a solid |
Crystal lattice energy increase as the _____ |
charge density increases |
Charge density = ____ |
ionic charge / ionic radius in angstrums |
four different ways to categorize solids |
- molecular
- network covalent
- ionic
- metallic |
characterized by relatively strong intramolecular bonds between the atoms that form the molecules |
molecular solids |
solid in which conventional chemical bonds hold the subunits together |
network solids |
salts that are held together by the strong force of attraction between ions of opposite charge |
ionic solids |
force of attraction in ionic solids depends on ____ |
square of the distance between the positive and negative charges |
solids that do not have a regular structure |
amorphous solids |
temperature at which the lattice of a solid collapses into a liquid |
melting point |
energy required to melt a solid |
enthalpy of fusion |
conversion of a solid into a vapor |
sublimation |
used to show the relationship between phases of matter and the P and T |
phase diagrams |
indicates the condition at which all 3 phases coexist in equilibrium |
triple point |
homogenous mixture of two or more substances in a single phase |
solution |
component present in a larger amount in a solution is called the _____ |
solvent |
Molarity |
Mols/liters of solution |
molality |
mols/kilo solvent |
Mole fraction |
(X) moles of component A divided by total moles |
Weight percent (% w/w) |
mass of one component divided by total mass of the mixture x 100 |
the concentration of solute in equilibrium with undissolved solute in a saturated solution |
solubility |
A solution in which undissolved and dissolved particles are in equilibrium is |
saturated |
more solute can be dissolved in the solvent |
unsaturated |
higher than saturated concentration of solute |
supersaturated |
the ability of one liquid to dissolve into another |
miscibility |
when two liquids do not form a solution but exist in contact with each other such as oil and water |
Immiscible |