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17 Cards in this Set

  • Front
  • Back

Rate determining step

slowest step in any proposed mechanism

Collision Theory of Chemical Kinetics

the rate of a reaction is proportional to the number of collisions per second between the reacting molecules

Effective Collision

-occurs when molecules collide in the correct orientation and enough energy to break existing bonds and form new ones

Activation Energy

-E(a), or energy barrier


- minimum energy of collision necessary for a reaction to take place

Rate of reaction eqn

rate = Z * f




Z= total # of collisions per sec


f = fractions of effective collisions

Arrhenius eqn

For collision theory




k= Ae^(-E/RT^2)




k= rate constant of a rxn


A = freq factor


E(a) = Activation Energy


R = ideal gas constant


T = Temp (K)



Freq Factor

-"attempt freq"


- measure of how often molecules in a certain reaction collide (s^-1)

Transition state theory

- "activated complex"


-where old bonds break and new bonds begin to form


- has higher energy than reactants and products


- will dissociate into products

Free energy of a reaction

- difference btwn free energy of the products and free energy o the reactants


- (-) = exergonic --> energy given off


- (+) = endergonic --> energy absorbed

Factors affecting rxn rate

- Reaction concentrations: more reactants, more collisions per unit time


- Temperature: rate increases with increasing temp (increasing KE)


-Medium: generally polar solvents are preferred due to their molecular dipoles polarizing the bonds of the reactants making them longer and weaker to speed up the rxn


-Catalysts: increase rxn rate without being consumed within the rxn but lowering E(a)



Determination of rate law

- for all forward, irreversible rxns, rate is proportional to concentration of reactants


- measured in molarity/sec


- rate = k[A]^x[B]^y


- k = rate constant


- x & y = orders of the rxn

Zero- order rxns


- rate of formation of product C is independent of changes in concentrations of any of the reactants A & B.


- rate law = k[A]^0[B]^0 = k (M/s)


- only way to change rxn is by temp or catalyst


- rxn vs. time = linear graph (slope = -k)


First order rxn


- rate is directly proportional to only one reactant (doubling reactant concen. doubles prod formation)


- rate = k[A]^1 or =k[B]^1


- plotting [A] vs. t = nonlinear


- plotting ln[A] vs. t = linear (slope = -k)


Second Order Rxn

- rate is proportional to either the concentrations of two reactants or to the square of the concentration of a single reactant.


- rate = k[A]^1[B]^1 or =k[A]^2 or = k[B]^2


- plotting [A] vs. t = nonlinear


- plotting 1/[A] vs. t = linear (slope = k)

Electrical Potential Energy


dependent on the relative position of one charge with respect to another


- like charges = +


- opposite charges = -


- U = kQq/r

Electrical Potential


ratio of the magnitude of the charges electrical potential energy to the charge itself


- V = U/q (J/C)


OR


-V = kQ/r


- scalar quantity


- sign determined by Q


- positive charges will move to decrease electrical potential (Voltage)


- negative charges will move to increaser their electrical potential (Voltage)

Potential Difference

-"Voltage"= Vb-Va = W(ab)/q


- W(ab) = work needed to move test charge q thru electric field from a to b.