Chem kinetics pt 1 L13

Question 1

Two imp things of a chem reaction

Answer 1

*How far it goes (thermodynamics)
*How fast it goes (kinetics)

TWO ARE NOT RELATED

Question 2

What are the two parts to studying kinetics?

Answer 2

Experimental and Theoretical

Question 3

Experimental

Answer 3

measure reaction rates i.e measure speed and study the factors that influence them i.e what speeds/slows down a reaction

Question 4

Theoretical

Answer 4

understand rates in molecular terms i.e what makes a reaction inherently fast/slow and use the exp data to probe reaction mechanisms

Question 5

What is a reaction mechanism?

Answer 5

intermediate steps that a reaction takes to reach completion

Question 6

What do we ask in a rate of reaction?

Answer 6

How does concentration change over time

Question 7

To quantify a curved rate of reaction:

Answer 7

Find the gradient of the reactant over time, this is called a rate

Question 8

What does a -ve rate mean?

Answer 8

We cannot have a negative rate so this means that the conc. is decreasing (the -ve sign in front of a term of reactant)

Question 9

For general reaction:

Answer 9

aA + bB –> cC + dD

rate = -1/a (dA)/dt = 1/c (dC)/dt

Question 10

Factors that affect the rate of reaction

Answer 10

*Chem nature
*Physical states of the reactant + products
* Conc.
*temp

NOT INVOLVED IN STOIC - no net change
*Catalyst
*inhibitor

Question 11

How does conc. of reactants affect the rate?

Answer 11

*Conc. of reaction increases then speed increases
*Conc. of reaction increases but no affect on speed eg u drink too much beer but ur body only processes a certain amount in time

Question 12

Rate law, order and constant

Answer 12

Rate law: rate = k [A]ˆx [B]ˆy

Question 13

What does rate law say?

Answer 13

If you change the conc.,this is how it will change the rate

Question 14

Can i ignore stoic for rate law

Answer 14

YAS

Question 15

How to determine rate law?

Answer 15

Through experiments as we cannot find x and y without it

Question 16

What is x and y

Answer 16

x - order with respect to A
y = order with respect to B
x + y = total order of reaction

Usually integers from 0 - 2

Question 17

what do 1st order reactions do?

Answer 17

Behave the same

Question 18

How to get 1st order reactions?

Answer 18

*1st order in A where reaction has only one reactant
*1st order in A where reaction has 2+ reactants but all other reactants are 0

Question 19

Pseudo 1st order reaction

Answer 19

Increasing the conc. of B in a reaction so that its conc. is relatively constant i.e it is not being used up much so we can write rate exp in terms of one reactant

k’ = k[B]

Rate = k’[A]

Question 20

Purpose of a pseudo 1st order reaction

Answer 20

Easier to find the rate by working with only 1 reactant (forcing the other reactant to not change)

Question 21

Rate of order changes with conc.

Answer 21

• 0 order - change in conc. has no affect on rate change
• 1st order - rate doubles

*2nd order - rate increases by 4 = k[A]ˆ2
rate increases by 2 = k[A][B]

Question 22

Rate constant k

Answer 22

*Independent of conc.
*increases with temp
*Gives constant of proportionality
*units depend on overall x+ y

Question 23

units when order = 0

Answer 23

mol-1s-1

Question 24

units when order = 1

Answer 24

s-1

Question 25

units when order = 2

Answer 25

L mol-1s-1

Question 26

units when order = 3

Answer 26

Lˆ2 mol-2 s-1

Question 27

Relationship between rate and time

Answer 27

Inverse relationship

Question 28

How does the rate constant change

Answer 28

If the order changes

Question 29

What is the isolation method?

Answer 29

Varying the conc. of one reactant and holding the others constant