Chapter 12 kinetics

Question 1

kinetics

Answer 1

the study of the ratewith which a chemical reaction occurs, the factorsthat affect the reaction rate, and the mechanismof reaction.

Question 2

concentrations as a Function of Time

Answer 2

The reactantconcentration decreases(consumed), and the productconcentration increases(formed) with time.2NH3(g) →N2(g)+ 3H2(g)

Question 3

rate of a reaction

Answer 3

is a measure of the speedat which a reaction occurs (mol/L • s)– always positive; samefor reactants or products.– expressed as the change in concentration of reactants (−)or products (+) divided by the change in tim

Question 4

Generic Reaction:

Answer 4

aA+ bB→cC+ dDA and B are reactants, C and D are products;a, b, c, and dare the stoichiometric coefficients

Question 5

average rate of reaction:

Answer 5

ate of a chemical reaction computed as the ratio of a change in concentration to the time interval over which the change occurred

Question 6

nstantaneous rate of reaction:

Answer 6

ate of a chemical reaction at any instant in time, determined by the slopeof the line tangential to a graph of concentration as a function of time.2NH3(g) → N2(g)

Question 7

nitial rate

Answer 7

instantaneous rate of a chemical reaction at t = 0 s (immediately after the reaction has begun)

Question 8

Rate law:

Answer 8

mathematical expressions that describe the relationship between the rateof a chemical reaction and the concentration of its reactants

Question 9

•n= 0

zero order

Answer 9

The unit of k: M • s−1

rate= k (A)o = k

Question 10

n=1

1st order

Answer 10

units: s-1

rate = k(a)1=k(a)

Question 11

n=2

2nd order

Answer 11

unitz; : M−1• s−1

rate= k(a)2

Question 12

Determining a rate law from initial rates:

Answer 12

1. Select two sets of experimental rate data that differ in the concentration of only one reactant 2. Set up a ratioof the two rates and the two rate laws. 3. After cancelingterms that are equal, we are left with an equation that contains only one unknown4. We then solve this equation for the order.

Question 13

•The rate laws

Answer 13

shows the relationship between therateof areaction and theconcentrationsof the reactants.– How reaction rate depends on concentration of reactant
rate= k(a)n

Question 14

•The integrated rate law

Answer 14

for a chemical reaction is an equation that relates the concentration of a reactant to elapsed timeof reaction– How concentration of reactants depends on reaction time. – The integrated forms of the rate laws

Question 15

half-life (t1/2) of

Answer 15

f a reaction is the time required for one-half of a given amount of reactant to be consumed.

Question 16

half life zwero order

Answer 16

depeding on initual concentration

Question 17

half life 1st order

Answer 17

independent of intial concentration

Question 18

half life seconf order

Answer 18

depending on intial concentration

Question 19

collision theory

Answer 19

model that emphasizes the energyand orientationof molecular collisionsto explain and predict reaction kinetics

Question 20

Three postulates for collision theory:

Answer 20

1. The rate of a reaction is proportional to the rate of reactant collisions: ∝ࢋ࢚ࢇ࢘ ࢔࢕࢏࢚ࢉࢇࢋ࢙࢘࢔࢕࢏࢙࢏࢒࢒࢕ࢉ #ࢋ࢓࢏࢚2. The reacting species must collide in an orientationthat allows contact between the atoms that will become bonded together in the product.3. The collision must occur with adequate energyso that the electrons of reactants can be rearranged and form new bonds and new chemical species.

Question 21

Activated complex:

Answer 21

unstable combination of reactant species representing the highest energy state of a reaction system– transition state, reaction intermediate, not final product

Question 22

Activation energy (Ea)

Answer 22

The minimumenergy necessary to form a product during a collision between reactants.

Question 23

Arrhenius equation:

Answer 23

mathematical relationship between the rate constant and the activation energy of a reaction

• Ea: activation energy (J/mol)
• R: 8.314 J/(mol • K)
• T: temperature in kelvins
• A: frequency factorࢋ

Question 24

Collision theory:

Answer 24

model that emphasizes the energyand orientationof molecular collisionsto explain and predict reaction kinetics

Question 25

Overall reaction

Answer 25

shows the startingsubstances and the endingsubstances.

Question 26

elementary reaction.

Answer 26

Overall reaction can be broken down into several steps, and each step is called

Question 27

Reaction Mechanism

Answer 27

s the process, or pathway, by which a reaction occurs

Question 28

Reaction intermediate

Answer 28

is a species that are produced in one step and consumed in a subsequent step (eg: O). – It doesn’t show up in the overall reaction

Question 29

Molecularity

Answer 29

of an elementary reaction is the number of reactantspecies (atoms, molecules, or ions).

Question 30

–Unimolecular:

Answer 30

oneparticle; A-products

Question 31

–Bimolecular

Answer 31

twoparticles (same or different); A+ B =products

Question 32

Termolecular:

Answer 32

threevparticles (same or different); A+ B + C =products

Question 33

Rate-determining step

Answer 33

s the slowestelementary reaction in a reaction mechanism; determines the rate of the overall reaction– like the narrowest section on a freeway

Question 34

To validate a mechanism, threeconditions must be met:

Answer 34

The elementary steps must sum to the overall reaction.2.The rate law predicted by the mechanism must be consistent with the experimentally observed rate law.3.Each elementary step should have an order of three or less

Question 35

Catalyst:

Answer 35

a substance that increasesthe rate of a chemical reaction but is not consumed by the reaction.– Catalysts function by providing an alternative mechanism that has a lower activation energy, and therefore a higher reaction rate.