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thermodynamics
energies of the reaction at equilibrium
mechanism
step by step pathway from reactants to products
kinetics
variation of reaction rates with different conditions and concentrations of reagents
chlorination of methane
methane + chlorine + heat/light ---> chloromethane +hydrogen chloride blue color absorbed by chlorine, activating it so it initiates reaction with methane high quantum yield
Free radical chain reaction
1. iniation step 2. propogation step 3. termination steps
mechanism
generates reactive intermediate
propagation
reactive intermediate reacts with a stable molecule to produce another reactive intermediate and product molecule allows chain to continue until supply of reactants is exhausted or reactive intermediate destroyed
termination
side reactions that destroy reactive intermediates and tend to slow or stop the reaction
initiation
generates reactive intermediate blue light splits chlorine into 2 unpaired electron is radical electron
PROPAGATION I
when chlorine collides with a methane molecule it removes hydrogen from methane, forming HCl bond and CH3 methyl radical
Propagation II
Methyl radical reacts with molecule of chlorine to form chloromethane chlorine atom is left with odd electron results in chloromethane and chlorine radical
Termination reactions
step that produces fewer reactive intermediates than it consumes -combination of any two free radicals -collision with wall
Equilibrium constant
a+b > c+d products /reactants keq > 1 reaction is favored, left to right keq<1 reaction moves right to left from value of keq we can calculate gibbs free energy
gibbs free energy
change in free energy (delta G) free energy of products - free energy of reactants if products < reactants reaction is favored (-delta G) -Delta G, energy released
Equilibrium constants and free energy
Keq= e^-DeltaG/(RT) DeltaG= -2.303RT(logv10Keq R-8.314 T-temp in kelvin e-2.718
delta H
enthalpy, heat change products - reactants measure of strength of bonding in products and reactants, reactions favor products with lowest enthalpy (strongest bonds) -delta H, heat released +delta H, heat absorbed
delta S
entropy products - reactants disorder reactions favor greatest entropy + denotes freedom of motion
change in free energy
delta G= delta H - Tdelta S
Bond dissociation energies
Bond breaking requires energy (+) bond forming releases energy (-) BDE always positive/endothermic delta H= (BDE of broken bonds) BDE bonds formed
homolytic
each bonded atom retains one of the bonds two electrons forms free radicals
heterolytic
one of the atoms retains both e-s forms ions enthalpies rely heavily on solvent to solvate ions that result
kinetics
study of reaction rates how fast
rate of rxn
how fast products appear and reactants disappear depend on concentrations of reactants, greater concentration-more likely to react rate = kr[a]^a[b]^b MUST BE DETERMINED EXPERIMENTALLY
activation energy
Ea minimum kinetic energy molecules must have to overcome repulsions between electron clouds when they collide `
Rate limiting step
transition states are at energy maximums intermediates are at energy minimums the reaction step with the highest activation energy will be the slowest, and the rate determining for the entire reaction
Rate, Ea, and temperature
Increasing Ea, rate decreases Increasing temp. rate increases fluorine reacts explosively chlorine reacts moderately bromine must be heated to react iodine does not react
carbanion
strongly nucleophilic species with negatively charged carbon atom having only three bonds C atom has nonbonding pair of electrons 8e- on C +lone pair, negative charge
carbene
highly reactive species with only two bonds to an uncharged carbon atom with a nonbonding pair of electrons carbon is neutral
carbocation
6 electrons, positive charge carbon sp2 hybridized with vacant p strongly electrophilic species with positively charged carbon atom only having three bonds opposite of carbanion
Hammond postulate
species closer in energy are also closer in structure in exo - transition state closer to reactants in energy in energy and structure in endo- transition state is closet to products in energy snd structure
inductive effect
donation or withdrawal of electron density through sigma bonds
intermediate
molecule or molecule fragment formed in a reaction and exists for finite length of time before it reacts in the next step corresponds to relative minimum in the diagram
radical inhibitor
compound added to prevent progogation of free radical chain rxns mostly stabilizes radicals so they dont react
resonance stabilization
takes place by delocalization of electrons in pi bonded system cations, radicals, anions often stabilized through this
reactive intermediates
carbocations free radicals carbanions carbene
inductive effect
donation of anelectron density along sigma bonds
hyperconjugatio
overlap of sigma bonding orbitals with empty orbital

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