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MCAT 2015 Chemistry (Examkrackers)
Terms in this set (148)
principle quantum number (n)
the shell; corresponds roughly to the energy level of the electrons within that shell; value: 1,2,3...
azimuthal quantum number (l)
the subshell; it gives the shape so recall that s orbitals are spherical and p orbitals are dumbbell-shaped; value: 0,1,..., n-1. subshell shapes are s,p,d, and f
magnetic quantum number (ml)
the specific orbital within a subshell; value: -l to +l. 3D orientation is Px, Py, Pz
spin quantum number (ms)
distinguishes between 2 electrons in the same orbital; one is spin +1/2 and other is spin -1/2
heisenberg uncertainty principle
states that there is an inherent uncertainty in the product of the position of a particle and its momentum. This is due to the dual nature (wave-particle) of matter. It is on the order of Planck's constant (6.6x10^-34 J.s)
building-up principle; new electron added must occupy lowest energy available
elements with unpaired electrons, meaning that a subshell is not completely filled. The spin of each unpaired electron is parallel to the others, and as a result, the electrons will align with an external magnetic field.
elements with no unpaired electrons, meaning their subshells are completely filled; they are unresponsive to external magnetic field
increasing the frequency of each photon --> increases the kinetic energy of the electron. If a single photon does not have sufficient energy, no electron will be emitted. The minimum amount of energy required to eject an electron is called the work function.
KE (excess) = hf (energy in) - work function (electron out)
All "E's" - electronegativity, electron affinity, and ionization energy are UP and to the RIGHT.
Atomic radius follows the opposite trend - that is, DOWN and to the LEFT.
bond length in relation to energy
the energy necessary for a complete separation of the bond is given by the vertical distance on the graph between energy at the bond length and zero (this is the bond dissociation energy)
kinetic versus thermodynamic control
the thermodynamic product -->more stable, a higher energy input, and produced slowly.
The kinetic product --> less stable, formed more quickly because lower energy input.
criteria for collision to initiate a reaction
1. the relative kinetic energies of colliding molecules must be greater than or equal to activation energy
2. proper orientation of molecules
A is the product of collision frequency, z, and fraction of collisions having effective spatial orientation, p, Ea is the activation energy and R the gas constant. Rate constant k of a reaction increases with higher pressure, temperature, and catalysts.
temperature dependence of reaction rates
the proportion of collisions (area under the curve) with energy greater than Ea will increase as temperature increases
measured as the disappearance of reactants or the appearance of products
m and n are the reaction orders of each reactant, sum of m and n is the overall order, and k is the rate constant for the forward reaction.
zero order reaction
first order reaction
rate of the slowest elementary step determines the rate of the overall reaction
4 possible variables:
1) the initial amount of substance
2) the final amount of substance
3) the half life
4) the number of half-lives
types of radioactive decay
number of hybrid orbitals must equal number of sigma bonds and lone pairs
sigma and pi bonds
____ bonds have lower energy, but are stronger and more stable. ___ bonds have higher energy, but decreased strength and stability.
if the conjugate base of an acid exhibits ___, it is more stable (and therefore a weaker base). A more stable conjugate base corresponds to a stronger acid. Phenol, whose conjugate base is ____-stabilized, is a stronger acid than ethanol.
increased stability of a cyclic molecule due to electron delocalization (resonance). These compounds must be cyclic, planar, and follow Huckel's rule, which states that planar monocyclic rings with 4n+2 pi electrons (where n is any integer, including zero) will be ____.
____ functional groups have a partial negative charge and seek positively charged nuclei. They donate electrons and usually "attack" groups with partial positive charges. They are also called Lewis bases.
____ functional groups have a partial positive charge and seek electrons. They usually get "attacked" by electrons from other groups. Because they are electron acceptors, they are also lewis acids.
____ have the same chemical and physical properties except for two cases:
1. interactions with other chiral compounds
2. interactions with polarized light
___ with multiple chiral centers have the same absolute configuration at one or more of those centers. They differ in their physical properties (rotation of plane-polarized light, mp, bp, solubilities, etc.) and in their chemical properties.
optically active isomers
the maximum number of ______ that a single compound can have is related to number of its chiral centers, n.
max. # = 2^n
diastereomers that differ in configuration at only one chiral center (e.g. galactose and glucose)
cyclic diastereomers that are formed when a ring closure occurs at an epimeric carbon (think carbohydrates)
cis/trans (geometric) isomers
have different physical properties. ___ molecules have dipole moment, and thus stronger intermolecular forces leading to higher boiling points. However, they have lower melting points than their respective ___isomers.
nucleophilicity vs. leaving group ability
the best nucleophiles are strong bases, and the best leaving groups are weaker bases.
properties: boiling and melting points of ___ are much higher than similar-size alkanes due to their ability to hydrogen bond. Branching generally lowers boiling point. They can act in 3 types of reactions as nucleophiles, acids, and as leaving groups when protonated.
electron withdrawing groups
strongly electronegative and pull electron density away from rest of the molecule, and stabilize negative charge.
electron donating groups
donate electrons and thus stabilize positive charge.
formation of alkyl halide from an alcohol
synthesis of a tosylate
useful for protection of alcohols
cleavage of an ether
often used as a solvent for organic reactions
reactivity of carbonyls
The more positive charge on the carbonyl carbon, the more likely it is to be attacked by a nucleophile. When EWGs are attached to it, it becomes even more positive and reactive. When EDGs are attached, the carbon becomes less positive and less reactive.
alcohols react with esters in a reaction called ____
formation of a lactone
an intramolecular ester is called a ____.
cyclic amides can be formed in intramolecular reactions and are called ____.
aldehydes and ketones
___ and ___ are more polar and have higher boiling points than alkanes of similar weight. They cannot hydrogen bond with one another, so they have lower boiling points than corresponding alcohols.
shift from a carbonyl to an alkene with an alcohol. It is a reaction at equilibrium; these structures are not resonance structures
kinetic vs. thermodynamic enolate
formed by the removal of acidic alpha hydrogens. The kinetic reaction has a lower activation energy but forms a less stable product. The thermodynamic reaction benefits from use of high heat.
formation of acetal/ketal
nucleophilic addition under acidic conditions
nucleophilic addition under basic conditions
protection of aldehydes/ketones
formation of imines/enamines
grignard synthesis of an alcohol
reduction synthesis of alcohol
formation of cyanohydrins
increase in bonds to oxygen or halogen, loss of C-H bonds
increase in bonds to hydrogen or R groups, loss of bonds to oxygen or halogen
oxidizing and reducing agents
-These include K2Cr2O7, K2MnO4, H2CrO4, O2, PCC
-These include LiAlH4, NaBH4, H2 + pressure
hydrolysis of carboxylic acid derivatives
formation of glucose
water is removed from the molecules; aka acetal formation in ochem
1. nitrogen acts as nucleophile and substitutes the bromide on diethyl-bromomalonate
2. hydrogen leaves the middle carbon of diethyl-bromomalonate. This carbon becomes a carbanion and is very nucleophilic - stabilized by carboxylic acids on either side
3. nucleophilic carbon undergoes SN2 with a new alkyl halide to add a R group to the amino acid
4. nitrogen is hydrolyzed from the phthalimide by acid and water to form a free amino acid
1. cyanide anion acts a nucleophile toward the carbonyl. However, nitrogen is better nucleophile than oxygen, and acid protonates the alcohol group
2. an aminonitrile is formed
3. strong acid in water protonates the nitrile group, turning it back into its carboxylic acid form. Molecule is now amino acid.
saturated and unsaturated fatty acids
melting point tends to increase with molecular weight and ____ have lower melting points (kinks and don't solidify as easily) than ___ acids, which are straight and solidify more easily.
hydrolysis of a phosphodiester bond
represents the amount of molecular movement in a substance - which can be divided into translational, rotational, and vibrational (sum of these is thermal energy). Any increase in thermal energy increases ____.
____, k, is related to the ideal gas constant R by Avogadro's number N.
R = Nk; k=1.38x10^-23 J/K.
average kinetic energy of a single molecule
K.E. = (3/2)*kT
average kinetic energy for a mole of molecules
K.E. = (3/2)*RT
internal energy, temperature, pressure, volume, enthalpy, entropy, and gibbs energy
includes all the possible forms of energy within a system, not counting the motion or position of the system as a whole
___ is the spontaneous transfer of energy from a warmer body to a cooler body
"two systems in thermal equilibrium with a third system are in thermal equilibrium with each other"
thermal energy transfer via molecular collisions. It requires DIRECT physical contact. In ____, higher energy molecules of one system transfer some of their energy to the lower energy molecules of the other system via molecular collisions.
thermal energy transfer via fluid (liquid or gas) movements. In _____, differences in pressure or density drive warm fluid in the direction of cooler fluid.
thermal energy transfer via electromagnetic waves. The rate at which an object radiates waves (its power P) depends on its temperature and surface area:
P = σεA(Te^4 - To^4) where σ is the stefan-boltzman constant (5.67 x 10^-8) and ε = emissivity of the object's surface
any energy transfer that is not heat.
w = -P∆V (constant pressure)
first law of thermodynamics
the total energy of the system and surroundings is always conserved. Any energy change to a system must equal the sum of heat flow into the system and work done on the system.
standard enthalpy of formation
the change in enthalpy for a reaction that creates one mole of that compound from its raw elements in their standard states
heat of reaction
second law of thermodynamics
"the entropy of an isolated system will never decrease"
third law of thermodynamics
No system can reach absolute zero.
Gibbs free energy
∆G = ∆H-T∆S
∆G = ∆G° + RT*ln(Q)
At equilibrium, ∆G = 0 by definition, so ∆G° = -RT*ln(K).
If K = 1 then ∆G° = 0
If K > 1 then ∆G°<0
If K < 1 then ∆G°>0
Hess' Law of Heat Summation
"the sum of the enthalpy changes for each step is equal to the total enthalpy change regardless of the path chosen"
the condition where the forward reaction rate equals the reverse reaction rate; no net change in the concentrations of products/reactants; it's the point of greatest entropy
equilibrium constant (K)
the _____ will not change for a given reaction unless the temperature changes; concentration of pure liquid or pure solid is 1
reaction quotient (Q)
products over reactants (same as K)
kinetic molecular theory
in the _____, an ideal gas lacks certain real gas characteristics:
1. gas molecules have no size (zero molecular volume)
2. gas molecules do not exert forces on one another
3. gas molecules have completely elastic collisions
4. the average kinetic energy of gas molecules is directly proportional to the temperature of the gas
Ideal gas law: PV=nRT
simple mercury barometer
the amount of mercury left in the tube is related to atmospheric pressure pushing down on the mercury bath by:
Patm = ρgh
PV = constant; volume and pressure are inversely related
V/T = constant; the volume of gas is directly proportional to temperature
V/n = constant; the volume of a gas is proportional to the number of moles at constant temperature and pressure
w =0, ∆E = q; no change in volume, then no work done!
process where no heat is transferred between the system and the surroundings; q = 0, ∆E = w
no change in internal energy; ∆E = 0, 0 = q + w
____ of a particular gas is the total pressure of the gaseous mixture multiplied by the mole fraction of the particular gas.
states that the total pressure exerted by a gaseous mixture is the sum of the partial pressures of each of its gases
Van der Waal's equation
Low temperature and high pressure lead to crowding of molecules
Vreal > Videal
since molecules of real gas do have volume, their volume must be added to the ideal volume, which is calculated from PV=nRT.
Preal < Pideal
Since the predominant intermolecular forces in a gas are attractive, gas molecules are pulled inward toward the center of the gas, and so strike the container wall with less force than predicted by KMT.
the added energy required to increase the temperature of a substance by one Kelvin (or degree celsius). A substance with a greater ______ can absorb more heat with less temperature change.
C = q/∆T
a container that holds a liquid, often water, with a thermometer placed inside to measure any changes in temperature.
heat of fusion
enthalpy change associated with melting
heat of vaporization
enthalpy change associated with boiling
solid -> liquid = melting
liquid -> solid = freezing
liquid -> gas = vaporization
gas -> liquid = condensation
solid -> gas = sublimation
gas -> solid = deposition
-Forming and breaking of intermolecular bonds. Intermolecular bonds remain the same in all phases.
-triple point: the only point where a substance can exist in equilibrium between solid, liquid and gas phases
-critical point: fluid beyond this point has characteristics of both gas and liquid, and is called supercritical fluid
[(mass of solute)/(total mass of solution)]*10^6
moles of solute divided by kg of solvent
pressure created by the molecules in the open space at equilibrium
a compound is ____ when the vapor pressure of its liquid phase is greater than the partial pressure of its gaseous phase.
when the vapor pressure of a liquid equals the atmospheric pressure.
a solute with no vapor pressure
solubility product (Ksp)
Ions that are present in a solution in which a reaction is taking place but that do not participate in the reaction.
common ion effect
the addition of a common ion pushes the equilibrium in the direction that will reduce the concentration of that ion, according to Le Chatelier's principle
C = solubility of gas (in moles per liter)
ka1= constant unique to solvent-solute pair
Pv= vapor partial pressure of gas above the solution
0 - atoms in their elemental form
-1 - fluorine
+1- hydrogen (except when bonded to a metal, like NaH, then -1)
-2 - oxygen (except when it is in a peroxide like H2O2; then -1)
reducing and oxidizing agent
The _____ gives electrons to another species (it itself is oxidized). The reverse is true for an ______.
used to find the molarity of a reducing agent. This involves titrating with a strong oxidizing agent and measuring the resulting voltage change.
standard hydrogen electrode
balancing redox reactions
aka voltaic cell; turns chemical energy into electrical energy. Components: T-E-I-E'-T', where T represents the terminals, E the electrodes, and I the ionic conductor (salt bridge). When the cell is formed, emf is the electric potential difference between T and T'.
a type of liquid junction that minimizes the potential difference in galvanic cell. A ___ is typically made from an aqueous solution of KCl, and allows the movement of ions between solutions without creating a strong extra potential within the cell.
∆G = -nFE
n is #moles of electrons transferred in the balanced redox reaction, F is charge on one mole of electrons (96,486 C/mol), voltage E
E = Eo - (RT/nF) log (Q)
At 298 K and in base 10 log form,
E = Eo - (0.06/n) log (Q)
a limited form of a galvanic cell in which a reduction half reaction takes place in one half cell while the exact reverse of that half is taking place in the other half cell. When we add these two half-reactions, we get E=0.
created by hooking up a power source across the resistance of a galvanic cell and forcing the reactions to run in reverse. It will have a negative emf.
lewis acid and base
A ___ is any substance that accepts a pair of electrons (molecules with incomplete octet, small cations with high charge) and a ___ as any substance that donates a pair of electrons.
arrhenius acid and base
An ___ is a substance that produces hydrogen ions in water, and an ____ is a substance that produces hydroxide ions in water. Only covers aqueous solutions.
bronsted-lowry acid and base
A ____ is any substance that donates a proton, whereas a ____ is any substance that accepts a proton.
strong acids and bases
_____: HI, HBr, HCl, HNO3, HClO4, HClO3, H2SO4
_____: NaOH, KOH, NH2-, H-, Ca(OH)2, Na2O, CaO
pH = -log [H]
autoionization of water
Consider the reaction: HA + H2O -> H3O+ + A-
the point where exactly one half of the acid has been neutralized by the base. Concentration of acid is equal to concentration of its conjugate base. [HA]=[A-]
a weak acid whose conjugate base is a different color. An ____ is used to find the equivalence point in a titration. Use one with a pKa that is as close as possible to the pH of the titration's equivalent point
the point where the indicator changes color is called the _____.
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