kinetics Flashcards
kinetics
study of rates of reactions
activation energy (Ea)
kinetic energy required for reactants to collide in order for the reaction to occur
what does the rate of a reaction correspond to
how many collisions take place over a given time
Arrhenius Equation
K= Ae^(-Ea/RT)
k is rate constant
k in arrenius eqn
rate constant
a in arrhenius eqn
frequency factor
- frequency of collisions between reactants
Ea
activation energy
R is arrhenius eqn
gas constant
the rate constant can only be meaningfully affected by waht?
Ea and T
If Ea/RT decreases what happens to k
rate constant decreases
larger values of -(Ea/RT)
more negative, inverse relationship between Ea and K
lower EA
higher rate of reaction
temperature relationship to reaction rate (k)
proportional
Ea relationship to reaction rate
inverse
two ways to speed up a reaction
- reduce Ea
- heat up
what other ways is K impacted
- concentration of reactants
- pressure in gas rxn (increase pressure increases rate)
transition complex
brief period where covalent bonds in the reactants begin to weaken and bonds of products begin to form
Ea relationship to transition complex
Ea is the amount of energy needed to reach the transition complex
what is the highest energy point of the reaction
transition complex
are transition complexes isolatable?
no, too unstable
rate limiting step of a reaction
slowest step
x axis of reaction coordinate diagrams
progress of reaction (time)
y axis of reaction coordiate diagrams
energy
Ea on reaction coordinate diagram
difference in E between reactants and highest point
∆G on reaction coordinate diagram
difference in E between reactants and products
energy of P<R
exergonic and ∆G< 0
endegonic reaction on reaction coordinate diagram
P energy > reactant
∆G>0
∆G
thermodynamic constant for a reaction that cannot be changed by kinetic parameters
- decides spontaneity
catalysts
substances that increase the rate of reaction by reducing the Ea
how do catalysts decrease Ea
by stabilizing the transition state
weaken bonds in reactants and change orientation to increase frequency of collisions
T/F catalysts can affect thermodynamic parameters
no. they do not change ∆G or sponteneity
heterogeneous catalys
different phase than the reactant
homogenous catalyst
same phase as reactant
rate law
rate= K[A]^x[B]^y
- units of M/s
order of a reaction
defined by the sum of the exponents
zero order reaction
exponents of reactants sum to 0
1 order reaction
exponents sum to one
second order rxn
exponents of reactants sum to two
third order rxn
exponents of reactants sum to three
how to determine rate
look at changing concentrations to see how they affect the rate
if the reactant is doubled and the rate is doubled what is the order
[A]^1
if the reactant is doubled and the rate is quadroupled what is the order
[A]^2
how to find K if you know the rates of both reactnats
K = rate/ [a]^x * [b]^y
units of k for 0 order
m*s^-1 or m/s
units of k for 1order
1/s
units of k for 2 order
1/(m*s)
units of k for 3 order
1/(m^2s)
zero-order reactions
enzymes are saturated and there is too much reactant per enzyme
- catalyst is rate limiting step
- concentration of reagents is irrelevant
first order reactions
radioactive decay and SN1 (depend on carbocation )
second order raections
involve collision between two reactant molecules as in SN2
second order raections
involve collision between two reactant molecules as in SN2
rate law formula is based on
initial rate of the reaction
graph of zero order rxn
linear
graph of first order
non linear
