Kinetics Flashcards
Energy barrier to reaction pathway
Activation energy
Transition state
Local energy maxima, unstable
Intermediate
Local energy minima, stable and can be isolated
Rate
-d[reactant]/dt or d[product]/dt
Rate at time t
Found with tangent of either graph of [product] against t or -[reactant] against t
General rate of
aA + bB → cC + dD
-1/ad[A]/dt
-1/bd[B]/dt
1/cd[C]/dt
1/dd[D]/dt
Differential rate equation
k[A]^m[B]^n
Pseudo-rate equation
When B is in large excess compared to A, [B] is roughly constant
Rate=k’[A]^m, where k’=k[B]^n
Method of initial rates
Initial rate=k’[A]0^m
Taking logs gives linear equation
Zeroth order integrated rate law
[A]=[A]0-kt
First order integrated rate law
[A]=[A0]e^(-kt)
ln[A]=ln[A]0
Second order (rate=k[A]^2) integrated rate law
1/[A]=1/([A]0)+kt
Second order (rate=k[A][B]) integrated rate law
ln(([B]/[B]0)/([A]/[A]0))
First order half life
ln(2)/k
Second order half life
1/([A]0k)
Arrhenius equation
k=Ae^-(Ea/RT)
Activation energy
Minimum energy reacting molecules must have to overcome an energy barrier to reaction
Catalyst
Provides an alternate pathway of lower activation energy, dramatically decreases value of k
Rate at eqm
0
Rate determining step
Slowest step with highest activation energy
Kinetic control
Ratio of product concentrations depends on the rate coefficients and hence the different activation energies
Irreversible conditions
Thermodynamic control
Depends on the eqm constants and hence the standard free energies
Reversible conditions
Competitive enzyme inhibition
Substrate and inhibitor can not bind at the same time
