Kinetics Flashcards
Factors that Affect Reaction Rates
Physical state of reactants (increase surface area=increase # collisions)
Concentration of reactants (increase reactant=increase # collisions)
Temperature (increase temperature=increase KE=increase in # collisions and energy of collisions
Presence of a catalyst (decrease activation energy=require less energy for collisions)
Rate of appearence
change (B)/ Change (time) or -rate of disappearance of A
Rate of disappearance
change (A)/ Change (time)
Average Rate
Change in concentration over a specific time interval
Instantaneous Rate
Rate at a particular moment during the reaction
Initial Rate
Instantaneous rate at t=0
Rate Expression
Compares the rate of reactants and products relative to each other and relative to the overall rate of the reaction
Rate Law
Shows that rate depends on the concentration of reactants
Rate=
k A^m B^n
k= rate constant
m, n: reaction orders
Rate constant, k, depends on…
Temperature and a catalyst
Overall reaction orders =
m + n
Units of rate constant, k, depends on…
reaction order
Units of Rate Constant Chart
Units of Rate Constant Chart
Rate constant, k, does not depend on
Concentration
Plots of the Different Orders
Zero order-concentration vs. time
First order-ln concentration vs. time
Second order-1/concentration vs. time
Zero Order
Rate is independent of concentration
slope=-k
Rate Law: rate=k
Integrated Rate Law: [At]=-kt+[A0]
Half Life: t1/2=[A0]/2k
First Order
Rate depends on concentration of a single reactant
slope=-k
Rate Law: rate=k[A]
Integrated Rate Law: ln[At]=-kt+ln[A0}
Half Life: t1/2=0.693/k
Second Order
Rate depends on the concentration of [A^2] or [A] and [B]
slope=k
Rate Law: rate=k[A^2]
Integrated Rate Law: 1/[At]=kt + 1/[A0]
Half Life: t1/2= 1/k[A0]
Half Life
Time required for reactant to reach 1/2 initial value
In zero and second order, the half-life depends on the initial concentration
First order is constant
Elementary Reaction
A process in a chemical reaction that occurs in a single event or step
Can use stoichiometry to find rate law
Can involve simultaneous collision of three or more particles but rare
Elementary steps of a multistep mechanism adds up to overall chemical equation
To find rate law for an overall reaction
you must use experimental data
Reaction Mechanism
The process by which a reaction occurs
The Collision Model
Molecules must collide in order to react
Increase # collisions = increase rate
The Orientation Factor
Collisions must occur with molecules in the proper orientation for a reaction to occur