4. Rate-determining step

Question 1

a reaction mechanism is

Answer 1

series of steps

make up the overall reaction

Question 2

the rate determining step is

Answer 2

slowest step in reaction mechanism (of a multistep reaction)

Question 3

an intermediate species is

Answer 3

formed in one step of a multistep reaction
is used up in the subsequent step
is not seen as a reactant or product in the overall equation

Question 4

(predicting reaction mechanisms from rate equation)

the molecules in the rate equation…

Answer 4

influence the rate = involved in rate determining step

Question 5

(predicting reaction mechanisms from rate equation)

reaction mechanisms include…

Answer 5

2 steps
slow rate determining step and fast step / other step

species involved in 2 steps cancel each other out to form overall equation

Question 6

(orders and the rate determining step)

order of the reactant in the rate equation tells us

Answer 6

how many molecules of it are involved in the determining step
e.g rate = k [CH3Br]
rate determining step involves just 1 molecule of CH3Br
rate = k [CH3Br]2
rate determining step involves 2 molecules of CH3Br

Question 7

for a mechanism to be valid

Answer 7

RDS must be consistent with rate equation

sum of steps must make overall equation

Question 8

what does rate determining step dictate

Answer 8

how quickly the reaction can proceed.

when measuring rate of reaction you are measuring the rate of rate determining step.