Kinetics Flashcards
The rate of a reaction is defined as a ____ quantity. ____ is included in the rate.
positive, stoichiometry
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.
slope, concentration, decreases
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 __ ___.
reactants, products, concentrations, temperature, catalyst, inhibitor, reaction mechanism
Often the rate doubles for every ____ °C rise in T
10
K is the rate constant which is always ___ and a function of _____. It may also depend on ___
positive, temperature, concentration
The reaction rate does ___ need an experiment while the __ ___ does.
not, rate law
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 __ ___
rate, concentration, reaction order
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 ____
power, sum, negative, fraction
Chemists often discover patterns in reaction rate data by examining the __ ___ of the reaction. Here, the concentration of the ___ are initially zero
initial rate, products
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 __ ___.
concentration, time, surface, -ak, solid catalyst
An integrated rate law gives the concentration of reactants or products at any ___ after the start of the reaction.
time
The time it takes for the reaction to consume half the reactant
half-life
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.
exponentially, ln[a]
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
rate constant, independent
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
low concentration, 1/[A]
The half life for a second order reaction is __ __ to the concentration of the reactant
inversely proportional
For an nth order reaction, t1/2 is proportional to ___. The units of k are equal to _____
[A]0^1-n, M^1-n s^-1
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
14C/12C, 14C first order, 5750, scintillation counter
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
log, inverse, Ea/R, Ea, A
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.
high, low, 0
In collision theory, two basic assumptions are made: 1. Molecules or atoms must ___ to react, 2. the collision must provide enough ____.
collide, energy
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
speed, cross section, concentration, squared
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.
kinetic energy, Ea
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 ___ ____.
fraction, shaded area, increases, e^(-Emin/RT), boltzmann distribution
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 ___ ___.
NaP(sigma), mean speed, collisional cross section, steric factor
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
relative orientation, half angle 30°, H
In summary, the collision theory states that the rate is equal to the ___ x ______
rate of collision, fraction with sufficient energy
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.
gas phase, arrhenius, jostle, vicinity
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.
transition state theory, maximum, bonding patterns, activation barrier, reaction profiles
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
energy, solvent, activation energy, hypothetical
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
simplest, elementary, reaction mechanism
The rate law of an elementary reaction can be determined ___ an experiment. For ____ reactions, the order of a reactant does not depend on _____
without, non-elementary, stoichiometry
A single molecule shakes itself apart of its atoms into a new arrangement (possible involving inert collisional partners) e.g. isomerization
unimolecular reaction
Two molecules or atoms collide and exchange energy, atoms, or groups of atoms, or undergo some other kind of change.
Bimolecular reaction
Three molecules or atoms are involved in the elementary process, very unlikely (slow) in the gas phase but quite common in liquids
termolecular reaction
When temperature is increased the __ ___ of an endothermic reaction increases more, hence the equilibrium constant ___, with greater yield of ___
forward rate, increases, product
When T is increased, the ____ rate of an exothermic reaction increases more, hence the equilibrium constant ____ with ____ yield of product
reverse, decreases, smaller
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 _____
product, reverse, equilibrium, concentration, constant, net formation, k1/k-1
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 ______.
K1, k2, reverse, K=k1/k-1 x k2/k-2
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
parallel, rapid, reactants, k/k’, constant
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
faster, intermediate, steady state approximation
the slowest step in the reaction path that governs the rate of the overall reaction
rate determining step
If the reaction can be ___ by a ___ reaction, the slowest step is no longer the rate determining step
sidestepped, parallel
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 ____
induction, intermediates, negligibly small, reactant, product, fast reacting, over
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 ____
reactants, products, equilibrium, pre-equilibrium
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
highly reactive, reactive species, chain carrier, radical, radical chain reaction, branching
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.
initiation, chain carrier, heat, light, propagation, reactant, termination
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
lindemann mechanism, reaction order, pressure, first order, second order
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
catalyst, chemical, activation energy, small, chlorofluorocarbons, ozone layer, radicals
____ __ 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.
heterogenous catalysts, honeycomb ceramic support, poisoned, inactivated, adsorption, lead, unleaded gasoline
__ ____ 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 __ ___
homogenous catalyst, balanced equation, rate law
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.
equilibrium constant, thermodynamic properties
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 ____ ___.
proteins, homogenous, substrates, enzyme concentration
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
enzyme-substrate complex, free, bound
Km is the __ ___ which is characteristic of a particular enzyme. It is equal to the concentration of substrate left at __ the __ ___
michaelis constant, half, maximum rate
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
vmax (constant), saturated, zeroth, [ES]
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
first, E, S
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 ___ __ ___.
molecularity, reactant molecules 1, 2, 3, rate determining step
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.
25-125, break, physical processes, viscosity
Parallel reactions are prevalent for reactions in ___ subject to ___. Consecutive reactions are prevalent in ___ reactions and __ ____.
solutions, catalysis, enzymatic, radioactive decay
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.
completion, forward, backward, concentrations, kf/kb = [B]eq/[A]eq, elementary reactions
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].
maximum, 0, faster, k1/k2, smaller
In elementary steps the __ = the order of the reaction and they sum to give the _____ of the overall reaction.
molecularity, stoichiometry
