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Level 88

Van Der Waals Equation


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What is the necessity for the Van Der Waals Equation?
equation that is a modification of the ideal gas equation to compensate for the behavior of real gases
What two factor does the Van Der Waals equation adjust for in the ideal gas law!
Volume - takes into account that the actual molecule takes up some of the volume in the container
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- Give equation
PV nRT
Vander Waals Equation
(P+n^2a/V2)(V-nb) = nRT
Deviations are greater if? (name 2 conditions )
Intermolecular attractive forces (IMF) of gas molecules are greater.
cvpolarity
seperation of charge, an asymmetrical difference in electronegativity along a bond or in a molecule
symmetrical
non-polar molecules are symmetrical or asymmetrical?
what are van der waals forces
small, weak, interactions between molecules (intermolecular)
what are intramolecular forces
bonds within molecules, stronger then intermolecular, polar/nonpolar covalent, ionic, etc.
electrostatic attraction
electrons of one atom are attracted to another atom's nucleus (partial positive attracted to partial negative)
what evidence do we have for VDW forces?
non-polar molecules can form gases, liquids and solids
dipole-dipole
forces that exist between polar molecules where the positive end of one molecule attracts the negative end of the other;
dipole-induced dipole
polar-nonpolar, a dipole can induce a temporary dipole to form in a nonpolar molecule, the molecules then line up to match partial positive and partial negative, weak and short lived
Dispersion Forces
All molecules are attracted to 1 another because the electrons of each molecule are attracted to protons of nuclei of nearby molecules.
hydrogen bonding
- the force of attraction between the hydrogen atom of one molecule and an unshared electron pair on F, O, or N
hydrogen bonding and water
hydrogen bonds keep water in the liquid phase over a wider range of temps than is found for any other molecule of its size, accounts for high boiling point
expansion of ice (example of hydrogen bonds)
ice expands when water freezes, most substances contract when freezing, 3.98 degrees celcius=mas density of water (liquid)
hydrogen bonds and ponds freezing
solid water (ice) has a lower density then liquid water, ponds freeze from top down, insulating water below, keeping pond from freezing solid
surface tension
a measure of how difficult it is to break the surface of a liquid
what causes surface tension?
cohesive forces between malecules are shared w/ neighboring atoms, since surface has no neighboring atoms above, they exhibit stronger attractive forces for neighbors next and below them
explain capillary rise
water rises up capillary tube because there are unbalanced forces between water & glass and the water & gravity
adhesion
an attraction between molecules of different substances
cohesion
attraction of molecules to each other
which molecules evaporate?
high energy molecules, taking high temperature/ energy away lowers total kinetic energy (temperature) of entire system
boiling and air pressure
boiling occurs when vapor pressure=barometric pressure, (when vapor pressure=760mmHg, boiling point=100 degrees celcius)
sweating
breaking water's bonds has cooling effect, high enrgy molecules are lost, when liquid evaporates takes energy
clay containers
porous clay, high energy molecules escape leaving lower temperature water
Vapor pressure
Force exerted by vapor particles directly above a liquid
evaporation vs. boiling
EVAPORATION: occurs at any temperature, high energy molecules escape, BOILING: occurs when atmospheric pressure=vapor pressure
volatile substances
easily evaporate, weak attractive forces, low boiling point, high vapor pressure
non-volitile substances
do not easily evaporate, strong attractive forces, high boiling point, low vapor pressure
equillibrium
when rate of forward reaction is equal to the rate of reverse reaction
conditions for equilibrium
closed system, rate of forward reaction=rate of reverse reaction, constant temperature pressure and color, both reactants and products are present (but not neccessarily in equal amounts)
melting point
temperature at which a compound turns from a solid to a liquid or a liquid to a solid
Boiling Point
??T bp = Kbp • m • i
Water Vapor
The gas form of water(H2O).
VSEPR theory
a theory that predicts some molecular shapes based on the idea that pairs of valence electrons surrounding an atom repel each other
tetrahedral
3 dimensional shape showing one central atom with 4 atoms coming off of it. Tetra means four!
pyramidal
a molecule with one unshared pair and 3 atoms coming off of a central atom. Ex: NH3
Bent Triatomic
Has 2 atoms bonded to the central atom with 2 unshared pairs. The bond angle is 104.5°. Ex. H₂O
Linear Triatomic
Has 2 atoms bonded to the central atom and no unshared pairs. Ex. CO₂
trigonal planar
a molecule whose shape is triangular and in one plane; ex: BH3, BF3
trigonal bipyramidal
Bond Angle - 90°, 120° and 180°
Linear diatomic
CN=2 LP-1
polar molecule
A _______ is one whose centers of positive and negative charge do not coincide. Thus, a polar molecule has a positive side and a negative side.
Molecular Symmetry
All atoms bonded to the central atom must be the same, all possible bonding sites are occupied with the same atoms, and there are no unshared pairs.
Non Polar Molecule
No partial charge is created, but it may contain polar covalent bonds.
van der Waals forces
a slight attraction that develops between the oppositely charged regions of nearby molecules; weakest of intermolecular attractions
Volatile
Easily evaporates at room temperature.
sigma bond
a bond formed when two atomic orbitals combine to form a molecular orbital that is symmetrical around the axis connecting the two atomic nuclei
pi bond
A bond formed when parallel p orbitals overlap creating two regions of electron density, one above and one below the internuclear axis.
Dipole-Dipole Interaction
The attraction between polar molecules, also known as dipoles. They attract because of the partial charges on neighboring molecules.
hydrogen bonds
attraction between molecules that have hydrogen bonded to a small, high en atom
London Dispersion Forces
Are caused by momentary dipoles that develop when random movement of electrons in a molecule results in an uneven distribution of electrons. They act between all atoms and molecules
Two Conditions
Increase pressure to compress the gas and decrease temperature to slow down molecular electron motion.
induced dipole
A non-polar molecule that has induced dipole due to nearby ion or molecule.
Intermolecular Forces (IMF)
potential energy between particles results from attractive and repulsive forces
Ion- Dipole
ion and polar molecule attract
Dispersion
Nonpolar-nonpolar, a temporary dipole forms in a nonpolar molecule which leads to a temporary dipole to form in another nonpolar molecule, weakest and shortest lived.
phase
state of matter; solids, liquids or gases
triple point
a temperature and pressure where matter can exist in all three phases at the same time
critical point
critical temperature+critical pressure
condensation
change from a gas to a liquid
vaporization
change from a liquid to a gas
freezing
change from a liquid to a solid
Melting (Fusion)
Solid to Liquid
deposition
Change from a gas directly to a solid
Sublimination
Solid to gas
Molecular Solid
lattice points occupied by individual molecules
Ionic Solid
unit cells contain particles with whole charges
Metallic Solid
powerful metallic bonding holds individual atoms together
Network Solid
strong covalent bonds link atoms together