Kinetics

Question 1

The rate of a reaction is defined as a ____ quantity. ____ is included in the rate.

Answer 1

positive, stoichiometry

Question 2

The reaction rate is the ____ of a tangent drawn to the graph of ____ as a function of time, divided by the relevant stoichiometric coefficient. For simple reactions, the rate typically ____ as the reaction proceeds.

Answer 2

slope, concentration, decreases

Question 3

Factors affecting rate include the nature of the ___ and the ____, the ___ of them, the _____, the presence of a ____, and the presence of an _____. All of these factors are linked to the __ ___.

Answer 3

reactants, products, concentrations, temperature, catalyst, inhibitor, reaction mechanism

Question 4

Often the rate doubles for every ____ °C rise in T

Answer 4

10

Question 5

K is the rate constant which is always ___ and a function of _____. It may also depend on ___

Answer 5

positive, temperature, concentration

Question 6

The reaction rate does ___ need an experiment while the __ ___ does.

Answer 6

not, rate law

Question 7

The units of k must be consistent with the ___ units which are usually expressed as ______ over time. Therefore the units of k depend on the __ ___

Answer 7

rate, concentration, reaction order

Question 8

The reaction order is the ___ to which the concentration of this component is raised in the rate law. The overall order of a reaction is the __ of the orders of all the components. The order of a reaction can be a ___ number or a ____

Answer 8

power, sum, negative, fraction

Question 9

Chemists often discover patterns in reaction rate data by examining the __ ___ of the reaction. Here, the concentration of the ___ are initially zero

Answer 9

initial rate, products

Question 10

Zeroth order reactions will produce a straight line when plotted in a ______ vs ____ plot. The slope equals ____ Reactions often take place at the surface of a __ ___.

Answer 10

concentration, time, surface, -ak, solid catalyst

Question 11

An integrated rate law gives the concentration of reactants or products at any ___ after the start of the reaction.

Answer 11

time

Question 12

The time it takes for the reaction to consume half the reactant

Answer 12

half-life

Question 13

In a first order reaction, the concentration of the reactant decays _____ with time. If we plot ___ as a function of time, we get a straight line with a slope of -ak.

Answer 13

exponentially, ln[a]

Question 14

the greater the __ ___, the shorter the half life of the 1st order reaction. The half life of a 1st order reaction is characteristic of the reaction and is ___ of the initial concentration

Answer 14

rate constant, independent

Question 15

A 2nd order reaction has a long tail of __ ___ at long reaction times. If we plot ___ against t, we get a straight line with slope -ak

Answer 15

low concentration, 1/[A]

Question 16

The half life for a second order reaction is __ __ to the concentration of the reactant

Answer 16

inversely proportional

Question 17

For an nth order reaction, t1/2 is proportional to ___. The units of k are equal to _____

Answer 17

[A]0^1-n, M^1-n s^-1

Question 18

Living plants and animals take in ____ in a fixed ratio determined by the natural abundance. When they die, no more ____ can be taken in and what is already in the body will decay follow ___ ___ kinetics, with t1/2 = _____ years. The age of an object can be determined using a sensitive __ ___ to detect the remaining radioactive 14C

Answer 18

14C/12C, 14C first order, 5750, scintillation counter

Question 19

Arrhenius found that when the __ of the rate constant was plotted against the ____ of the absolute temperature, an approximately straight line was obtained. The slope is ____. While k is a function of temperature, ___ and ____ are approximately independent of it and characteristic of the reaction being studied

Answer 19

log, inverse, Ea/R, Ea, A

Question 20

A ____ activation energy corresponds to a reaction rate that is very sensitive to T. A ___ activation indicates that the reaction rate varies only slowly with T. If Ea = ___ the reaction rate is independent of T.

Answer 20

high, low, 0

Question 21

In collision theory, two basic assumptions are made: 1. Molecules or atoms must ___ to react, 2. the collision must provide enough ____.

Answer 21

collide, energy

Question 22

To find the rate at which an atom or molecule collides, we must first answer what is the ___ of the molecule, what is the __ ___, and what is the _____. The rate of collision is given by the concentration ___, multiplied by the rest of the factors. divided by

Answer 22

speed, cross section, concentration, squared

Question 23

Collision theory says that a reaction only takes place when two molecules collide with a relative __ ____ of at least _____. If this energy is smaller, no reaction occurs.

Answer 23

kinetic energy, Ea

Question 24

In collision theory, the ____ of molecules, f that collide with a kinetic that is equal or higher to Ea for a reaction is given by the __ ___ under each curve. The fraction of molecules ______ as the temperature is raised. The fraction is equal to _____. This result comes from the ___ ____.

Answer 24

fraction, shaded area, increases, e^(-Emin/RT), boltzmann distribution

Question 25

In collision theory, the factor a is equal to __. where c is the __ __ at which molecules approach others in a gas, sigma is the __ __ __, the area that a molecule presents as a target during a collision, while P is the ___ ___.

Answer 25

NaP(sigma), mean speed, collisional cross section, steric factor

Question 26

P, the steric factor, and it takes into account the species’ ___ ____ in the gas phase, which will influence whether a reaction occurs or not. The best direction of attack in this reaction is within a cone of __ __ ___ surrounding the ___ atom

Answer 26

relative orientation, half angle 30°, H

Question 27

In summary, the collision theory states that the rate is equal to the ___ x ______

Answer 27

rate of collision, fraction with sufficient energy

Question 28

Although collision theory can in principle be made exact for any type of reaction, in practice it is only useful for ____ ___ reactions. Still, we can extend some of its concepts to explain why the __ equation also applies to reactions in solution. In solution, molecules do not speed through space and collide but ___ through the solvent and stay in one another’s ____ for relatively long periods of time.

Answer 28

gas phase, arrhenius, jostle, vicinity

Question 29

In activated complex theory, also called __ ___ ____, the energy increases as the reactant molecules approach each other and reaches ___ as they form an activated complex. It then decreases as atoms rearrange into __ __ characteristic of the products and these products separate. Only molecules with enough energy can cross the __ __ and react to form products. ___ ____ represent the energy changes during a reaction.

Answer 29

transition state theory, maximum, bonding patterns, activation barrier, reaction profiles

Question 30

in transition state theory, a reaction only occurs if two molecules acquire enough ___ perhaps from the surrounding ___ to form an activated complex and cross an energy barrier. The barrier height is approximately equal to the __ ____. The activation complex is a ___ species, not one that could be isolated

Answer 30

energy, solvent, activation energy, hypothetical

Question 31

The reason we cannot in general write a rate law from the chemical equation is that all but the _____ reactions are the outcome of several and sometimes many steps called ___ reactions. To understand how a reaction occurs, we have to propose a __ __, a sequence of elementary reactions as reactants are transformed into products

Answer 31

simplest, elementary, reaction mechanism

Question 32

The rate law of an elementary reaction can be determined ___ an experiment. For ____ reactions, the order of a reactant does not depend on _____

Answer 32

without, non-elementary, stoichiometry

Question 33

A single molecule shakes itself apart of its atoms into a new arrangement (possible involving inert collisional partners) e.g. isomerization

Answer 33

unimolecular reaction

Question 34

Two molecules or atoms collide and exchange energy, atoms, or groups of atoms, or undergo some other kind of change.

Answer 34

Bimolecular reaction

Question 35

Three molecules or atoms are involved in the elementary process, very unlikely (slow) in the gas phase but quite common in liquids

Answer 35

termolecular reaction

Question 36

When temperature is increased the __ ___ of an endothermic reaction increases more, hence the equilibrium constant ___, with greater yield of ___

Answer 36

forward rate, increases, product

Question 37

When T is increased, the ____ rate of an exothermic reaction increases more, hence the equilibrium constant ____ with ____ yield of product

Answer 37

reverse, decreases, smaller

Question 38

All reactions consist of a forward and reverse reaction. At the start of a reaction, when little or no ___ is present, the rate of the ____ reaction is negligible. All reactions proceed toward a state of ___ with time. In equilibrium, the ____ of the reactants and the products are ____, and there is no __ ___ of any substance (d(a)/dt = 0). Therefore, the equilibrium constant K for the elementary reaction is equal to _____

Answer 38

product, reverse, equilibrium, concentration, constant, net formation, k1/k-1

Question 39

When a reaction has a complex mechanism in which the elementary reactions have rate constants __ ___…., and vice versa for the ___ reactions, the overall equilibrium constant k is equal to ______.

Answer 39

K1, k2, reverse, K=k1/k-1 x k2/k-2

Question 40

In ____ reactions, a reaction can sometimes proceed by two or more independent paths. The most ___ path determines the predominant path, and the ____ disappear in parallel. Thus, the ____ which equals the ratio of the parallelly formed products will be ___ at any time of the reaction

Answer 40

parallel, rapid, reactants, k/k’, constant

Question 41

For consecutive reactions, if the second reaction is much ____ than the first, the second product never gets a chance to build up, and it becomes an ______. The ___ ___ ___ can be applied to it, and we can treat the system as just one reaction from the reactant to the second product

Answer 41

faster, intermediate, steady state approximation

Question 42

the slowest step in the reaction path that governs the rate of the overall reaction

Answer 42

rate determining step

Question 43

If the reaction can be ___ by a ___ reaction, the slowest step is no longer the rate determining step

Answer 43

sidestepped, parallel

Question 44

The steady state approximation assumes that after an initial __ period, an interval during which the concentrations of the ___ rise from zero, and during the major part of the reaction, the rates of change of concentration of all reaction intermediates are ___ ____. The intermediate is not a ___ or ___. it is a short lived, or __ ___ species that appears while the reaction proceeds, There is no intermediate left when the reaction is ____

Answer 44

induction, intermediates, negligibly small, reactant, product, fast reacting, over

Question 45

When the rates of formation of the intermediate and its decay back into the ___ are much faster than the rate of formation of the ____, one can assume that the reactants and the intermediate are in __ through the course of the reaction. this is called ____

Answer 45

reactants, products, equilibrium, pre-equilibrium

Question 46

In a chain reaction, the product of one step in a reaction is a __ ___ reactant in a subsequent step, which in turn produces ___ ___ that can take part in subsequent reaction steps. The highly reactive species is called the __ ___. If this is a ____ the reaction is called __ ___ ___. ____ chain reactions can be explosively fast

Answer 46

highly reactive, reactive species, chain carrier, radical, radical chain reaction, branching

Question 47

The first step in a chain reaction is ____. This is the formation of ___ __ from a reactant. __ or ___ is often used to generate the chain carriers. the second step is ___. One carrier reacts with a ___ to produce another carrier. The last step is ___, which is the elementary reaction that ends the chain reaction.

Answer 47

initiation, chain carrier, heat, light, propagation, reactant, termination

Question 48

The ____ ____ simply describes the change in __ __ of gas phase reactions. If there is a high ___ limit, then the second step is much faster than the third, and the reaction follows ____ behaviour. If there is a low pressure limit, the third step is much faster than the second and the reaction follows ____ behaviour

Answer 48

lindemann mechanism, reaction order, pressure, first order, second order

Question 49

A ____ is a substance that changes the rate of a reaction but undergoes not net ____ change. A catalyst can provide a new pathway with a lower __ ___. In many cases, only a ____ amount of catalyst is necessary because it acts over and over again. This is why small amounts of _____ can have such a devastating effect on the __ __ in the stratosphere. They break down to ____ that catalyze the destruction of ozone

Answer 49

catalyst, chemical, activation energy, small, chlorofluorocarbons, ozone layer, radicals

Question 50

____ __ are catalysts that are present in a phase different from that of the reactants. An example is the catalytic converter of a car, which is made from a mixture of catalysts bonded to a ___ __ ___. The catalysts can be __ or ____. A common cause is the ___ of a molecule so strong that it seals the surface of the catalyst. Some heavy metals, especially ___, are very potent poisons for catalysts, thus the use of ___ __ in automobiles fitted with catalytic converters.

Answer 50

heterogenous catalysts, honeycomb ceramic support, poisoned, inactivated, adsorption, lead, unleaded gasoline

Question 51

__ ____ are catalysts that are in the same phase as the reactants. Although a catalyst does not appear in the __ __ the concentration of a homogenous catalyst does appear in the __ ___

Answer 51

homogenous catalyst, balanced equation, rate law

Question 52

Catalysts do not change the ____ ___ of a reaction. Kinetics also does not change the ____ __ of chemical reactions such as enthalpy, internal energy, gibbs free energy, etc.

Answer 52

equilibrium constant, thermodynamic properties

Question 53

Enzymes are biological molecules (mostly ___) that catalyze the reactions necessary to life. They are ___ catalysts. ___ are the molecules on which the enzymes act to promote biochemical reactions. The rate is always proportional to the total ____ ___.

Answer 53

proteins, homogenous, substrates, enzyme concentration

Question 54

In the steady state approximation for enzyme kinetics, the rate of the ______ _____ is set to zero. The total enzyme concentration is usually known and is equal to the sum of the __ and ___ enzyme concentrations

Answer 54

enzyme-substrate complex, free, bound

Question 55

Km is the __ ___ which is characteristic of a particular enzyme. It is equal to the concentration of substrate left at __ the __ ___

Answer 55

michaelis constant, half, maximum rate

Question 56

When the concentration of the substrate is very large, Km + S is approximately S, and the rate = ____. This means that the enzyme sites are ___ with the substrate and the reaction is ___ order in [S]. The formation of the product from ___ is the rate determining step

Answer 56

vmax (constant), saturated, zeroth, [ES]

Question 57

When [S] is small, Km + [S] = Km, and the michealis menten equation becomes ___ order in [s]. Therefore, at low concentration of S, the rate of binding between _ and ___ (step one) becomes the rate determining step

Answer 57

first, E, S

Question 58

The ____ is defined in a theoretical mechanism and equals the number of __ ___ in a single elementary step. It is usually ___, ___ or rarely __. The molecularity of the overall reaction is taken to be that of the ___ __ ___.

Answer 58

molecularity, reactant molecules 1, 2, 3, rate determining step

Question 59

Typical Ea values for chemical processes are _____ kJ/mol because energies of this magnitude are required to ___ chemical bonds. Activation energies smaller than this represent __ __ like plastic flow or ___ changes.

Answer 59

25-125, break, physical processes, viscosity

Question 60

Parallel reactions are prevalent for reactions in ___ subject to ___. Consecutive reactions are prevalent in ___ reactions and __ ____.

Answer 60

solutions, catalysis, enzymatic, radioactive decay

Question 61

When products are not strongly favored over reactants, reactions do not go to ___. Both __ and ___ reactions continue to occur, but net ____ of all species are constant with time. This means Keq = ____. This equation is true for reversible ___ ___ of any order.

Answer 61

completion, forward, backward, concentrations, kf/kb = [B]eq/[A]eq, elementary reactions

Question 62

in consecutive reactions, the concentration of the first product always goes through a ___ which occurs when the d[first product]dt = ____. The ____ the second consecutive reaction is, in other words, the smaller the ratio of ____, the ___ the value of the maximum of the [first product].

Answer 62

maximum, 0, faster, k1/k2, smaller

Question 63

In elementary steps the __ = the order of the reaction and they sum to give the _____ of the overall reaction.

Answer 63

molecularity, stoichiometry