Kinetics

Question 1

Factors that Affect Reaction Rates

Answer 1

Physical state of reactants (increase surface area=increase # collisions)
Concentration of reactants (increase reactant=increase # collisions)
Temperature (increase temperature=increase KE=increase in # collisions and energy of collisions
Presence of a catalyst (decrease activation energy=require less energy for collisions)

Question 2

Rate of appearence

Answer 2

change (B)/ Change (time) or -rate of disappearance of A

Question 3

Rate of disappearance

Answer 3

change (A)/ Change (time)

Question 4

Average Rate

Answer 4

Change in concentration over a specific time interval

Question 5

Instantaneous Rate

Answer 5

Rate at a particular moment during the reaction

Question 6

Initial Rate

Answer 6

Instantaneous rate at t=0

Question 7

Rate Expression

Answer 7

Compares the rate of reactants and products relative to each other and relative to the overall rate of the reaction

Question 8

Rate Law

Answer 8

Shows that rate depends on the concentration of reactants

Question 9

Rate=

Answer 9

k A^m B^n
k= rate constant
m, n: reaction orders

Question 10

Rate constant, k, depends on…

Answer 10

Temperature and a catalyst

Question 11

Overall reaction orders =

Answer 11

m + n

Question 12

Units of rate constant, k, depends on…

Answer 12

reaction order

Question 13

Units of Rate Constant Chart

Answer 13

Units of Rate Constant Chart

Question 14

Rate constant, k, does not depend on

Answer 14

Concentration

Question 15

Plots of the Different Orders

Answer 15

Zero order-concentration vs. time
First order-ln concentration vs. time
Second order-1/concentration vs. time

Question 16

Zero Order

Answer 16

Rate is independent of concentration
slope=-k
Rate Law: rate=k
Integrated Rate Law: [At]=-kt+[A0]
Half Life: t1/2=[A0]/2k

Question 17

First Order

Answer 17

Rate depends on concentration of a single reactant
slope=-k
Rate Law: rate=k[A]
Integrated Rate Law: ln[At]=-kt+ln[A0}
Half Life: t1/2=0.693/k

Question 18

Second Order

Answer 18

Rate depends on the concentration of [A^2] or [A] and [B]
slope=k
Rate Law: rate=k[A^2]
Integrated Rate Law: 1/[At]=kt + 1/[A0]
Half Life: t1/2= 1/k[A0]

Question 19

Half Life

Answer 19

Time required for reactant to reach 1/2 initial value
In zero and second order, the half-life depends on the initial concentration
First order is constant

Question 20

Elementary Reaction

Answer 20

A process in a chemical reaction that occurs in a single event or step
Can use stoichiometry to find rate law
Can involve simultaneous collision of three or more particles but rare
Elementary steps of a multistep mechanism adds up to overall chemical equation

Question 21

To find rate law for an overall reaction

Answer 21

you must use experimental data

Question 22

Reaction Mechanism

Answer 22

The process by which a reaction occurs

Question 23

The Collision Model

Answer 23

Molecules must collide in order to react
Increase # collisions = increase rate

Question 24

The Orientation Factor

Answer 24

Collisions must occur with molecules in the proper orientation for a reaction to occur

Question 25

Activation Energy

Answer 25

Minimum energy to start reaction

Question 26

Collision Theory

Answer 26

Collide, have proper orientation, have suffient energy

Question 27

Change in energy does not relate to…

Answer 27

reaction rate

Question 28

Endothermic vs. Exothermic

Answer 28

Endothermic=energy is absorbed so products have greater energy than reactants
Exothermic=energy is given off so products have less energy than reactants

Question 29

The Arrhenius Equation

Answer 29

k=Ae^-Ea/RT
A: frequency factor, related to collisions and orientation
R: 8.314 j/molK

Question 30

Increase in temp or decrease in Ea will lead to…

Answer 30

increase rate constant

Question 31

Molecularity

Answer 31

of molecules that are reactants
Unimolecular= 1 molecule involved

Question 32

Intermediate

Answer 32

A substance that is formed in on elementary step but used in a later one so it doesn’t show in the overall reaction

Question 33

Catalyst

Answer 33

A substance that speeds up a chemical reaction; it is present at the start of reaction and re-foremed in a later step but does not show up in overall reaction

Question 34

How do you know that you are dealing with an elementary step?

Answer 34

It is a single step in a multi step mechanism or it tells you

Question 35

Which steps determines the rate of the overall mechanism?

Answer 35

Slowest step limits the overrallr eaction

Question 36

Mechanisms with a Slow Initial Step

Answer 36

Use coefficients from the slow step to get the rate law

Question 37

Mechanisms with Fast Initial Step

Answer 37

Write rate law for the last step
Write forward and backward rate law for the first step
Substitute for the compound backing up the reaction

Question 38

Peaks

Answer 38

Transition State/Elementary Steps

Question 39

Valley

Answer 39

Intermediates

Question 40

How do catalysts work?

Answer 40

They provide an alternate pathway with lower potential energy
Leads to new reaction mechanism
Leads to greater rate constant
-Formation of a more stable activated complex, increase collision frequency, improves the orientation of the reactantants

Question 41

Homogeneous Catalyst

Answer 41

In the same phase/state of matter as the reacting molecules

Question 42

Heterogeneous Catalyst

Answer 42

In different phase/state of matter than the reacting molecules

Question 43

Enzymes

Answer 43

Biological catalysts; usually proteins