ch 11-12

Question 1

chemical kinetics

Answer 1

the study of the speeds of chemical reactions and the factors that affect those speeds

Question 2

homogeneous

Answer 2

reactants and products are all in the same phase

Question 3

catalyst

Answer 3

a substance that increases the rate of a chemical reaction without being consumed like a reactant; changes the mechanism for the reaction; provides a lower Ea in the rate limiting step; does not change the products or their relative properties

Question 4

factors that control the speed of reactions

Answer 4

properties of the reactants and products(structures and type of bonding); concentration of reactants and products; temperature; presence of catalyst; nature of the surface

Question 5

rate

Answer 5

the change of some measurable quantity per unit of time

Question 6

reaction rate

Answer 6

the change in the concentration of a reactant or product per unit of time; a positive quantity

Question 7

average reaction rate

Answer 7

calculated from a change in concentration divided by a change in time

Question 8

instantaneous reaction rate

Answer 8

reaction rate at a particular time after the reaction has begun

Question 9

to find reaction rate

Answer 9

find the slope of the line tangent to the plot of the concentration versus time at the specific time plot of interest

Question 10

effect of concentration on rate

Answer 10

for many reactions as reactant concentration changes the rate changes
rate=k[reactant]

Question 11

rate law

Answer 11

mathematical expression that summarizes the relationship between concentrations and reaction rate

Question 12

rate constant

Answer 12

k; proportionality constant relating reaction rate and concentrations of reactants and other species that affect the rate of a reaction

Question 13

half life

Answer 13

the time it takes for one half of the reactant to be converted into product

Question 14

zeroth order

Answer 14

t1/2=[A]0/2k

Question 15

first order

Answer 15

t1/2=ln(2)/k

Question 16

second order

Answer 16

t1/2=1/k[A]0

Question 17

activation energy

Answer 17

Ea; the minimum energy that reactant molecules must have to be converted to product molecules

Question 18

transition state (activated complex)

Answer 18

a molecular structure corresponding to the maximum of a plot of energy versus reaction progress

Question 19

intermediate

Answer 19

an atom molecule or ion that is produced in one step of a reaction mechanism and used up in later step

Question 20

elementary reactions

Answer 20

are the reactions that occur at the molecular level

Question 21

unimolecular reactions

Answer 21

involve a single molecule or particle that rearranges into one or more different particles; cis-2-butene to trans-2-butene; always first order

Question 22

bimolecular reactions

Answer 22

involving two molecules or particles that collide and rearrange; iodide ions reacting with methly bromide; always second order

Question 23

Arrhenius equation

Answer 23

gives us the relationship between the rate constant, temperature and activation energy
k=Ae^-Ea/RT

Question 24

frequency factor

Answer 24

how often a collision occurs in the correct orientation

Question 25

complex reactions

Answer 25

do not occur as written; progress by a series of elementary steps

Question 26

reaction mechanisms

Answer 26

the combination of elementary steps that comprise a complex reaction

Question 27

rate-limiting step

Answer 27

the slowest elementary reaction in a complex reaction; the overall reaction will occur at the same rate

Question 28

heterogeneous catalyst

Answer 28

in a different phase from the reaction mixture

Question 29

homogeneous catalyst

Answer 29

in the same phase as the reaction mixture; usually more active; usually less stable

Question 30

enzymes

Answer 30

highly efficient biochemical catalysts; most active homogeneous catalysts

Question 31

chemical equilibrium

Answer 31

the point in a chemical reaction where reactant and product concentrations are constant; dynamic, independent of the direction of the approach, unaffected by the presence of catalysts

Question 32

dynamic equilibrium

Answer 32

reactants convert to products; products can also react to make reactants; equilibrium occurs when [A],[B],[C],[D] stop changing; species do not stop forming or being destroyed, rate of formation=rate of removal, concentrations are constant

Question 33

equilibrium constant

Answer 33

Kc=kfoward/kreverse=[C]^c[D]^d/[A]^a[B]^b

Kp=PcCPdD/PaAPbB

Question 34

Kc>1

Answer 34

reaction is strongly product favored; very little reactant; forward reaction only; goes to completion

Question 35

Kc

Answer 35

strongly reactant favored; very little product forms; no reaction

Question 36

Kc=1

Answer 36

reactants and products present at equilibrium

Question 37

reaction quotient

Answer 37

Q; can predict the direction of a reaction; whenever system is at equilibrium Kc=Q

Question 38

Q

Answer 38

Q must increase;; make more product; move foward

Question 39

Q>K

Answer 39

Q must decrease; less product; move back

Question 40

lechatelier’s principle

Answer 40

if the conditions of a system at equilibrium are changed so that it is no longer at equilibrium, the system wil react to reach a new equilibrium in a way that partially counteracts the change; system at equilibrium resist change

Question 41

Qc>Kc

Answer 41

shift to the left to consume some product and form more reactant

Question 42

changing pressure or volume

Answer 42

K does not change if P or V do not change; equilibrium position may change

Question 43

Volume doubled

Answer 43

lower concentration; more molecule, increase concentration; shift toward products

Question 44

pressure doubled

Answer 44

removing molecules, decrease P; shift toward reactants

Question 45

changing temperature

Answer 45

increase- minimize by removing heat; forward reaction is endothermic; equilibrium shift forward
decrease-offset by adding heat; reverse reaction is exothermic; equilibrium shift to left

Question 46

exothermic reactions

Answer 46

Kc decreases as T increases; less product favored

Question 47

endothermic reactions

Answer 47

Kc increases as T increases; more product favored