Chemistry Chapter 5 Chemical Kinetics And Equilibrium

Front 1

intermediate

Back 1

cancels itself out of a mechanism

Front 2

the slowest step in a rxn is the _______ step

Back 2

rate-determining

Front 3

if a step labels itself as "slow"....

Back 3

it is the rate determining step

Front 4

reactants have a ____ rate since they are being _____ in the process

Back 4

negative; consumed

Front 5

2A + B --> C

what are the rates?

Back 5

-1/2A = -B = C

Front 6

rate is expressed in....

Back 6

mol/L/sec or Molarity/sec

Front 7

2A + B ---> C

what is the ratio between A:C?

Back 7

1/2A = C
so....
A = 2C

Front 8

rate law

Back 8

rate = K[A]^x[B]^y

Front 9

the K constant is ______ upon temperature and changes with different temperature

Back 9

dependent

Front 10

the rate law; K[A]^x[B]^y
is only the rate of the ________

Back 10

reactants

Front 11

K[A]^x[B]^y
the x/y values are not:

Back 11

stoichiometric coefficients
only reactants

Front 12

for the reverse rxn, the Keq value would be....

Back 12

Kforward/Kreverse

Front 13

rxn rate is usually measured at the _____ of a rxn to minimize the effects of the reverse rxn

Back 13

beginning

Front 14

determining the x/y exponents in K[A]^x[B]^y

ex)
1 [A] = 1 [B] = 1 rate = 2
2 [A] = 1 [B] = 2 rate = 8.1
3 [A] = 2 [B] = 2 rate = 15.9

Back 14

([1/1]^x[2/1]^y) = 8/2

2^y = 4 ; y = 2

([2/1]^x[2/2]^y) = 16/8

2^x = 2 ; x = 1

so K[A][B]^2

Front 15

zero-order rxn

Back 15

K[A]^0[B]^0
rate = K

Front 16

zero order rxn: one whose rate of formation is _____ of changes to any of the reactants

Back 16

independent

Front 17

how can you change the rate of a zero order rxn if it is independent of the concentrations of the reactants?

Back 17

1. change the temperature and the K will change

2. add a catalyst; lowers Ea; increases K

Front 18

1st order rxns

Back 18

rate = K[A] or K[B]

Front 19

what is an example of 1st order rxn?

Back 19

radioactive decay

Front 20

what is the eq for radioactive decay?
[At] = ?

Back 20

[At] = [Ao]e^(-kt)
-occurs when molecule undergoes a chemical change by itself, without a chemical interaction, and usually without a physical interaction, with any other molecule

Front 21

second order rxns

Back 21

k = [A]^2 or [A][B] or [B]^2
suggests a physical collision between molecules

Front 22

mixed order rxns

Back 22

1. non-integer fractions(broken-order)
2. order(x/y) varies over the course of a rxn
--rxn changes over time

Front 23

collision theory of chemical kinetics

Back 23

rate of a rxn is proportional to the number of collisions per second between reacting molecules

Front 24

not all collisions result in a chemical rxn!

Back 24

know this

Front 25

collisions must be able to break bonds and form new ones

Back 25

know this

Front 26

activation energy Ea

Back 26

minimum energy needed to begin rxn

Front 27

rate = zf

Back 27

z = total collisions
f = fraction of collisions that are effective

Front 28

transition state

Back 28

formed when molecules collide with enough energy equal to the Ea; bonds are weakened and new ones form

Front 29

transition state has _____ energy than either the reactants or the products

Back 29

greater

Front 30

while in transition state, it can either go towards formation of ____ or _____

Back 30

reactants or products

Front 31

enthalpy (/\H)

Back 31

determines direction of rxn

Front 32

exothermic

Back 32

-/\H = release energy/heat; forward rxn preferred

Front 33

endothermic

Back 33

+/\H = requires energy/heat; prefers reverse rxn

Front 34

on the graph; enthalpy is the difference between the reactant and the product.

Back 34

know this...pg 119

Front 35

rxn rate factors

Back 35

reactant concentrations
temperature
medium
catalysts

Front 36

how do reactant concentrations affect rxn rate?

Back 36

greater the concentrations of reactants, the greater the number of collisions, rxn rate increases

**note; increase in rate will NOT occur for zero-order rxns since independent of concentrations!

Front 37

_____ for gas serves as a measure of concentration

Back 37

partial pressure

Front 38

how does temperature affect the rxn rate?

Back 38

rxn rate will increase as temperature increases

temperature increase avg. KE

Front 39

how does the medium affect the rxn rate?

Back 39

some molecules prefer h2o, DMSO or ethanol

-the physical state(S/L/G) can affect the rxn rate also

Front 40

_____ solvents are preferred as mediums because their molecular dipole tends to polarize the bonds of the reactants; lengthening and weakening them, permitting a faster rxn

Back 40

polar

Front 41

how do catalysts affect a rxn rate?

Back 41

increase the rxn rate without being consumed within the rxn

-reduce Ea
-enzymes = catalysts
-increase frequency of collisions
-donate electron density
-

Front 42

homogeneous catalysts

Back 42

same phase as reactants
(S/L/G)

Front 43

heterogeneous catalysts

Back 43

different phase than reactants

Front 44

catalysts have ____ impact on the Keq value

Back 44

NO

Front 45

irreversible rxn

Back 45

only occurs in one direction; product dependent upon limiting reactant

Front 46

reversible rxn

Back 46

reaction can occur in either direction; do not go to completion

Front 47

what is dynamic EQ?

Back 47

forward rate = reverse rate
no net change in concentrations

entropy is at is maximum level at EQ
free gibbs energy /\G is at a minimum

Front 48

law of mass action

Back 48

if a system is at EQ at a given temperature, then Keq is constant

Front 49

Keq =

Back 49

[products]/[reactants]

or [forward]/[reverse] rates!
concentrations

Front 50

reaction quotient

Back 50

same ad Keq equation...but usually compared to Keq to determine direction of the rxn

Front 51

reaction quotient vs Keq

Back 51

Qc = concentrations are changing and not in EQ

Front 52

Keq < Q

Back 52

favors reactants; spontaneous

disfavors products; non-spontaneous

Front 53

Keq > Q

Back 53

favors products; spontaneous

disfavors reactants; non-spontaneous

Front 54

Keq = Q

Back 54

equilibrium

Front 55

properties of law of mass action

Back 55

1. pure solids/liquids do not appear in the Keq/Q EQ
2. K = temperature dependent
3. Keq reverse = 1/Keq forward
4. larger Keq value signals further to completion

Front 56

le chatelier's principles

Back 56

concentration
temperature
pressure

Front 57

le chatelier's principles + concentration

Back 57

increase a concentration; rxn shifts to get rid of it

remove a concentration; rxn shifts to replace it

Front 58

le chatelier's principles + temperature

Back 58

increase temperature; rxn shifts to remove it

decrease temperature; rxn shifts to replace it

Front 59

le chatelier's principles and pressure

Back 59

increase pressure/ decrease volume; triggers decrease in volume, shifting rxn to form less molecules

decrease P/ increase V = want to increase P and shift rxn to form more molecules

Front 60

pressure changes only associated with ____ molecules since ___ and ____ are considered to be incompressible

Back 60

gas; solids/liquids

Front 61

temperature only affects Keq, not Q

Back 61

know this