Kinetics Flashcards
Rate
Difference in concentration over a given time
Half life
Time taken for concentration of reactant to half
Distinction between first and second order
2nd order slows down more rapidly than 1st order and for second order half life decreases as concentration decreases
Zero order
Plot [A] against t, half life decreases as [A] decreases
Multiple reactants
Rate law is additive eg two first order reactants gives second order overall
Isolated method
Way of measuring rate, arrange all concentrations in excess except one, excess concs reman ~ constant
Elementary reactions
Single step at molecular level, rate law determines by single probability and order = molecularity eg uni molecular
Unimolecular reaction
Elementary first order reactions of type A -> products, every A behaves independently so rate proportional to no of A molecules
Bimolecular reactons
Rate proportional to no of pairs of reactants
Rate determining step
Overall rate = rate of slowest sep
Rapid pre-equilibrium
Concs of some species remain in balance
Organic chemists rule of thumb
Rate of typical reaction doubles for every 10C increase around room temp
What does a larger value of Ea mean
K more sensitive to T
What’s the need for A in Arrhenius equation
Accounts for all factors that affect rate other than energy
Catalysts
Provide alternative route by decreasing activation energy
Counting rate of collisions
Collisions occur when impact parameter, b < ra+rb, has area = collision cross section, rate proportional to collision cross section, average relative speed of molecule and number density of molecules
What’s required for successful collisions
Do molecules collide with enough energy and do they collide n correct geometry
Transition state theory
Rate proportional to concentration of transition state ie chance of forming transition state
K++
Pseudo equilibrium constant for transition state, [AB++]/[A][B]
