Kinetics

Kinetics

study of reaction rates

stoichiometry- deals with amount of reactant & products

Collision Theory

• molecules must collide to react

• in order for a reaction to occur, there have to be effective collisions

  • sufficient energy

  • proper orientation

  • collide

• energy of collision > activation energy

Activation energy (E_a)

• energy reactants need to overcome (energy difference between the reactant and transition state)

Activated complex (transition state)

• arrangements of atoms found at the top of the potential energy state

• unstable- bonds breaking + forming

endo v exo

endo- product above reactant (+)

exo- product below reactant (-)

y- potential energy

x- reaction progress

ways to increase rate of reaction

1. stir mix

2. increase concentration (mol/L) (aq or gas)

3. increase surface area (s, l)

4. heat/ increase temperature

5. add a catalyst

   1. speed up reaction, not reaction, not consumed

   2. lowering activation energy by providing a new pathway- changing mechanism

Acid- base catalyst

• takes reactant either adds or takes protons away to speed up chemical reaction

• homogenous catalyst

surface catalyst (heterogenous catalyst)

• made up metal ( more SA- more active sites)

• increase number of successful collisions

• reaction intermediate

1. providing active site on their surface, gases absorbed onto metal

2. metal breaks bonds

3. both molecules migrate towards each other

4. form products (saturated mlc so can’t bind to metal and leaves)

enzyme

• homogenuous

• reaction intermediates- short lived species that is formed then consumed during multi step chem reaction

• speed up chem reaction, lower activation energy

• binds substrate to active site

homogenous catalyst

esterification: use to make flavorings

reaction rate

• change in concentration of a reactant/product per unit time

rate= (concentration A at t₂ - concentration A at t₁)/ t₂ - t₁

rate= Δ [A] / Δt

• if concentration decrease with time then negative

instaneous rate

value of reaction rate at a particular time

slope of tangent line= change in y/ change in x

first- order half life

• half- life is constant

explain why unlikely that reaction occurs in a single elementary step

unlikely that 4 molecules would all collide at the exact same moment, with the proper orientation and sufficient energy to overcome the activation energy barrier

what does increase temperature do

adds energy which increase collisions, with lower temp. there isn’t sufficient energy for high collisions

activation energy

as activation energy increase the reaction rate decrease, need to overcome greater barrier

E_a= E_ac - E_r

molecularity

molecularity greater than bimolecular has a very low probablity of occuring

• termolecular occur less than bimolecular

equilibrium

• some reactions are reversible

• we use double arrow

• at equilibrium the rate of the forward reaction is equal to the reverse reaction

• rate forward= rate reversed

• don’t want intermediate to show in rate law expression

equilibrium steps

how do you know how many steps from reaction profile

• number of peaks shows steps

• largest activation peak is the slow step