Kinetics

Question 1

Kinetics

Answer 1

is the study of how reactions take place and how fast they occur.
it tells us NOTHING about spontaneity of the reaction

Question 2

elementary steps

Answer 2

when the reaction happens in multiple steps these are called elementary steps, they show us the reaction mechanism

Question 3

intermediates

Answer 3

they don’t appear in the starting material or the products. the cancel out and don’t appear in the OVERALL equation
- intermediate is a substance that is produced in one elementary step and consumed in the subsequent step.

Question 4

Rate determining step

Answer 4

this is the slowest step in a process that determines the overall reaction rate

Question 5

rate

Answer 5

change in something over the change in time.

- how fast reactants are being used, or how fast products are being made.

Question 6

what effects the reaction rate?

Answer 6

reactant molecules must collide and interact in order for old bonds to break and new ones to form to make products. ANYTHING that affects their colliding and interaction can affect the rate of the reaction . therefore, the reaction rate is determined by :

1) how frequently the reactant molecules collide
2) the orientation of the colliding molecules
3) their energy

Question 7

what is the activation energy?

Answer 7

min energy needed of reactant molecules during a molecular collision in order for reaction to proceed to products.
if reactants don’t have this energy, the collisions won’t be able to make the products and reaction won’t occur.

Question 8

what happens when the reactants possess the necessary Ea?

Answer 8

they can reach a high energy and short lived TRANSITION STATE , also known as THE ACTIVATED COMPLEX.

Question 9

statements about the reaction rate

Answer 9

the lower the Ea the faster the reaction rate.
the greater the concentration of reactants the faster the reaction rate : as favourable collisions are more likely if the concentration of the reactants increase.
the higher the temp of the reaction mixture, the faster the reaction rate. - at higher temp, more reactant molecules have sufficient energy to overcome the Ea and molecule collide at a higher frequency so the reaction can proceed at a faster rate.

Question 10

thermodynamic factors and the kinetic factors

Answer 10

DO NOT affect each other!

Question 11

catalysts

Answer 11

provide reactants with a diff route , usually a shortcut to get to the products.
it either speeds up the RDS or provides an optimized route to the products.

Question 12

how does the catalyst accelerate the reaction?

Answer 12

it lowers the Ea of the RDS and therefore the energy of the transition state.
the catalyst remains unchanged at the end of the reaction.

Question 13

like intermediates catalysts are not included in the final overall reaction and ..

Answer 13

the catalyst is first a reactant and then a product.

intermediates are product first and then a reactant.

Question 14

addition of a catalyst will affect the rate of a reaction and not ?

Answer 14

the thermodynamics and the equilibrium!
so the thermodynamics and the equilibrium are not affected.
therefore no effect on delta G, H,S of the reaction

Question 15

Rate laws

Answer 15

on the exam, given rate of a reaction and asked to derive the rate law!
products are not included in rate laws- ONLY REACTANTS!

Question 16

what does the rate law tell us?

Answer 16

reactants part of the RDS are part of the rate law expression

Question 17

how can the rate law be determined?

Answer 17

ONLY experimentally! -exception to this rule is for an elementary step in a reaction mechanism that is the RDS.
the rate law is first order for a unimolecular elementary step and second order for a bimolecular step.

Question 18

the rate constant

Answer 18

the rate constant k can be figured out by rearranging the rate law .

the Arrhenius equation 
k= Ae^ -(Ea/RT) 
A: Arrhenius factor : takes into account the orientation of the colliding molecules. 
Ea: activation energy 
R: gas-law constant 
T: temperature in kelvins 
rewrite the equation as : 
lnK= lnA- (Ea/RT) 

if we add a catalyst, the EA is decreased.
increasing the temp will increase K .
if the expression Ea/RT decreases , subtracting something smaller give a bigger K

Question 19

units of the rate constant in the rate law expression

Answer 19

units of the rate constants are not uniform from one reaction to next. reactions of different orders will have rate constants bearing different units.
1st order : s-1
2nd order: M-1s-1
3rd order : M-2s-2