Chem Midterm 1 (10/21/08)

Front 1

what is kinetics?

Back 1

REACTION RATES, change of concentration of reactant and product over time

Front 2

average rate equation when aA+ bB--> cC +dD

Back 2

-1/a *Δ[A]/Δt =
-1/b *Δ[B]/Δt=
1/c *Δ[C]/Δt=
1/d* Δ[D]/Δt

it is the avg rate because the rate may not be the same at all of the times. (time period may change)

Front 3

why is A and B negative and C and D positive?

Back 3

A and B are reactants so they are used up and decrease

C and D are products and are produced

Front 4

how do you calculate instantaneous rate?

Back 4

instantaneous rate: reaction rate at a specific time on graph..

*LOOK at SHORTER INTERVALS*
rate= slope of the graph

****It turns out that the rate that is most useful is the instantaneous rate at the very beginning of the reaction--
this will tell us something about how the reaction goes before concentration changes much and we have to worry about back reactions etc.

Front 5

rate constant

Back 5

proportionality constant between reaction rate and concentration of reactant

Front 6

k= ratio
what does the rate constant depend on?

Back 6

temperature, solvent,

NOT
concentration

Front 7

rate law

Back 7

reaction rate to the rate constant and the reactant concentrations, which are raised to a power (determined experimentally)

Front 8

rate vs. order

Back 8

rate= k [A]^p [B]^q [C]^r [D]^s

order= p + q + r + s (either 0, 1, or 2)

Front 9

summary of rate law- (3)

Back 9

1. Rate laws are determined experimentally; the data should be given to you so that you can determine the reaction order and rate constant.
2. Always look at the [reactant] for reaction order, NEVER the products!
3. The coefficient of the reactants in the equation do not determine the orders.

Front 10

Half-life (t1/2):

Back 10

time required for the reactant concentration to decrease by half of its initial concentration

Front 11

zero order reaction

Back 11

A → Product
Rate=k[A]^0 = k

[A]t = -kt + [A]0
t1/2 = [A]0/2k

Front 12

first order reaction

Back 12

A→ Product
Rate=k[A]

ln [A]t = -kt + ln [A]0
ln ([A]t/[A]0) = -kt
t1/2 = 1/(k)ln2 = 0.693/k

Front 13

second order reaction (POSITIVE SLOPE)

Back 13

2A → Product
Rate=k[A]2
1/([A]t) = kt + 1/([A]0)
t1/2 = 1/(k[A]0)

Front 14

Arrhenius Equation

Back 14

k = Ae^-Ea/RT

Front 15

reaction mechanism

Back 15

a series of elementary steps representing the overall reaction, which includes intermediates and catalysts

Front 16

intermediates

Back 16

molecules appearing in the mechanism but not in the overall reaction

Front 17

catalysts

Back 17

substances increasing the reaction rate without being consumed by lowering the activation energy

Front 18

rate determining step

Back 18

the slowest step in the series: also determines the rate law

Front 19

chemical kinetics- collision theory

Back 19

reaction rate is proportional to the collision frequency

Front 20

thermodynamics equation- brush teeth

Back 20

ΔG = ΔH -TΔS

Front 21

ΔG = ΔG° + RT lnQ,
what is Q?

Back 21

the reaction quotient
Q = [C]^c[D]^d / [A]^a[B]^b

Front 22

what does k equal?

Back 22

products over reactants
[C]^c[D]^d/ [A]^a[B]^b

Front 23

what happens when k>1?

Back 23

less reactants, more products

Front 24

when k>1, what reaction does it favor?

Back 24

it favors the FORWARD reaction.
it favors the production of PRODUCTS

Front 25

what happens when k<1?

Back 25

more reactants, less products

Front 26

what reaction does k<1 favor?

Back 26

it favors the REVERSE reaction.
it favors the production of REACTANTS.

Front 27

when _____ , the reaction is spontaneous in what direction?

1.) ΔG<0
2.) ΔG>0
3.) ΔG=0

Back 27

1.) ΔG= negative, so in FORWARD direction

2.) ΔG= positive, so in REVERSE direction

3.) ΔG=0, so neither direction, because at equilibrium

Front 28

for a FORWARD rxn, when A+B--> C+D, what is the elementary step?

Back 28

rate= k[A][B]

Front 29

for a REVERSE rxn, when C+D--> A+B, what is the elementary step?

Back 29

rate=k[C][D]

Front 30

what is k equilibrium?

Back 30

kforward/ kreverse
[C][D]/[A][B]

Front 31

what is the thermodynamic definition of equilibrium?

Back 31

G=0

Front 32

le chatelier's principle

Back 32

an external stress applied to a system at equilibrium causes the system to adjust to partially offset the stress

Front 33

what is the differential rate law for the zero order reaction

what are the units?

Back 33

r = k

units= mole L-1 sec-1
mol/L*s

Front 34

what is the differential rate law for the first order reaction and what are the units?

Back 34

r = k [A]

units= sec-1
1/sec

Front 35

what is the differential rate law for the second order reaction and what are the units?

Back 35

r = k [A]2

units= L mole-1 sec-1
L/mole*sec

Front 36

what is the integrated rate law for zero order reaction?

Back 36

[A]_t = -kt + [A]_0

Front 37

what is the integrated rate law for first order reaction?

Back 37

ln{[A]} = -kt + ln{[A]_0}

A plot of ln[A] vs. time t gives a straight line with a slope of − k.

Front 38

what is the integrated rate law for the second order reaction?

what is the unit of k?

Back 38

1/[A]= 1/[A]_0+ kt

1/ M*s

Front 39

elementary reaction?

Back 39

reaction whose rate law can be written from its molecularity where molecularity is the number of species that must collide to produce the reaction of that step

Front 40

what are the three diff. types of elementary steps?

Back 40

1.) unimolecular: rate = k[A]
2.) bimolecular: rate= rate = k[A]^2
3.) termolecular

Front 41

what is one thing about mechanism?

Back 41

You can never prove the mechanism, you can only find a reasonable explanation that is consistent with the data.

Front 42

what is the rate determining step?

Back 42

The elementary reaction that is most important to consider is the slowest of the step—that is the one that will limit how fast the reaction can go and it is called the rate-determining step.

Front 43

intermediate?

Back 43

a chemical species produced early in the reaction, which is consumed later--so it is neither a reactant nor a product in the net reaction

Front 44

what does k depend on ?

Back 44

frequency and collision

Front 45

heterogenous catalyst?

Back 45

reactants and catalysts are in diff phases. usually the catalyst is solid and the reactants are either gases or liquids

Front 46

homogenous catalyst?

Back 46

reactants and catalyst are dispersed in a single phase, usually liquiid

Front 47

equilibrium?

Back 47

kforward [A][B]= kreverse [C][D]

forward is just as favorable as reverse

Front 48

forward rxn A+B--> C+D
reverse rxn C+D--> A+B

what are the elementary steps?

Back 48

rate= k[A][B]
rate= k[C][D]

Front 49

what is the thermodynamic definition of equilibrium?

Back 49

ΔG=0

ΔG ^0= -RT lnK
ΔG=ΔG^0 + RT lnQ

Front 50

Q= [C]^c[D]^d/ [A]^a[B]^b
K= [C]^c[D]^d/ [A]^a[B]^b

Back 50

q=k at equilibrium