Textbook Chapter 12- Kinectics Flashcards
rate of a chemical reaction
the rate of a chemical reaction is a measure of how much reactant is consumed, or how much product is produced, by the reaction in a given amount of time.
rate expression
the mathematical representation of the change in species concentration over time
reaction rates (3)
the change in the amount of a reactant or product per unit time.
Reaction rates are therefore determined by measuring the time dependence of some property that can be related to reactant or product amounts.
by convention positive
relative rates of reaction (3)
for homogenous reactions…
all related simply to one another according to the reaction stoichiometry.
For homogeneous reactions, both the reactants and products are present in the same solution and thus occupy the same volume, so the molar amounts may be replaced with molar concentrations:
factors affecting reaction rates (5)
concentration
temperature
catalyst
physical state (more sa is faster)
nature of participating substances
When reactants are in different physical states, or phases (solid, liquid, gaseous, dissolved), the reaction takes place only at
the interface between the phases
rate law
mathematical expressions that describe the relationship between the rate of a chemical reaction and the concentration of its reactants.
the forms m and n in rate law can be an what they are (2)
reaction orders
can be positive, negative, fraction or 0
K (2)
what is it independent off and dependant off
rate constant
independent of the reactant concentrations but does vary with temp and pressure
how is k m n determined in rate law
must be determined experimentally by observing how the rate of a reaction changes as the concentrations of the reactants are changed.
instantaneous rate (3)
a snapshot/rate at a specific time
defined as the slope of the tangent to the concentration vs time graph
the derivative of the curve at time t
the higher the order of the reactant
the more effect it has on the reaction
rate order of 0 indicates that+in rate equation (2)
the reactant has no affect on the rate
no need to write in rate law
method of initial rates (2)
measuring reaction rates for multiple experimental trials carried out using different initial reactant concentrations
An approach to determine rate law
How to find rate law 2 method with a table:
- find the row where the first reactant is constant but the second ist. See how the change in the second causes the change in the reaction rate (diving and see how much larger after the second reactant is doubled or sm)
do the same for first reactant - rate 3/rate2=k[1][2]/k[1][2]
and use the exponent which is m, n to find the value.
Integrated rate law (2)
+what you can use it for/Ex
relates the concentrations of reactants and time
We can use an integrated rate law to determine the amount of reactant or product present after a period of time or to estimate the time required for a reaction to proceed to a certain extent. For example, an integrated rate law is used to determine the length of time a radioactive material must be stored for its radioactivity to decay to a safe level.
deferential rate law integrated with respect to time=
not equation just general***
equation that relates the amount of reactant/product present in a rxn mixture to the elaspes time of the rxn
difference between differential rate law and integrated
The differential rate law tells you how the rate of a reaction depends on the concentration of reactant(s). The integrated rate law tells you how the concentration of reactant(s) depends on time
Integration of the rate law for a simple first-order reaction (rate = k[A]) results in an equaton……
+what is it?
in an equation describing how the reactant concentration varies with time:
integration of first order rate law…this equation may be rearranged to other formats, including direct and indirect proportionalities and linear dependance: (3)
graphing linear format of first degree+what if not straight line+formula (2)
A plot of ln[A]t versus t for a first-order reaction is a straight line with a slope of −k and a y-intercept of ln[A]0. If a set of rate data are plotted in this fashion but do not result in a straight line, the reaction is not first order in A.
According to the linear format of the first-order integrated rate law, the rate constant is given by
*not experimental execution u dumb
the negative of this plot’s slope.
what’s the axis for characteristic kinectic plot of first degree for integrated
ln[A]t vs t
Charactertosoc kinectic plot of secind degree
1/[A]t. vs t
rate unit in the rate law always equal to
mol/ls
so M/s=rate law units
rate law constant units between M(mol/L) and t
*M
M exponent keeps decreasing
you know an integrated rate law is second order reaction is___+line plotting equation
the plotted is a striaght line.
half-life of a reaction (t1/2)
the time required for one-half of a given amount of reactant to be consumed
zero order half life depends on
+equation
initial concentration and rate constant
First order half life
dependent on/not dependent on/ equation
depends only on K, independent on the concentration
Second order half life
formula, depends on
Depends on inital concentration and rate constant
In first order reactions what is the relationship between fast/short reactions and k value and half life?
Faster reactions exhibit larger rate constants and correspondingly shorter half-lives. Slower reactions exhibit smaller rate constants and longer half-lives.
For second order reaction what happens to half life as reaction proceeds?
the half-life increases as the reaction proceeds because the concentration of reactant decreases.
half-life of a zero-order reaction and initital concentration relationship
The half-life of a zero-order reaction increases as the initial concentration increases.
which rate order’s integrated rate law linear plot slope is positive?
2nd
What is the three thing collision theory is based on?
- The rate of a reaction is proportional to the rate of reactant collisions
- The reacting species must collide in an orientation that allows contact between the atoms that will become bonded together in the product.
- The collision must occur with adequate energy to permit mutual penetration of the reacting species’ valence shells so that the electrons can rearrange and form new bonds (and new chemical species).
What is the three thing collision theory is based on? (3)
- The rate of reaction is porprotional to the rate of reactant collisions
- The reacting species must collide in an orientation that allow contact between the atoms that will become bonded together in the product
- The collision must occur with adequate energy to permit mutual penetration of reacting species valence shell so that the electron can rearrange ad form new bonds
activated complex/transition state
an unstable species, very short lived and usually undetectable by most analytical instruments.
Explain to me the relationship between activation energy and kinectic energy
If the activation energy is much larger than the average kinetic energy of the molecules, the reaction will occur slowly since only a few fast-moving molecules will have enough energy to react. If the activation energy is much smaller than the average kinetic energy of the molecules, a large fraction of molecules will be adequately energetic and the reaction will proceed rapidly
reaction diagram general
Used in chemical kinetics to illustrate various properties of the reaction of interest. Viewing the diagram from left to right, the system initially comprises reactants only, A + B. Reactant molecules with sufficient energy can collide to form a high-energy activated complex or transition state. The unstable transition state can then subsequently decay to yield stable products, C + D.
activation energy Ea
energy difference between the reactants and transition state
enthalpy change
+what is exothermic?
the energy difference between the reactants and products
ΔH<0 is exothermic
Arehenius equation+equation
what R, A e means
relates the activation energy and the rate constant
R is the ideal gas constant, which has a value 8.314 J/mol/K, T is temperature on the Kelvin scale, Ea is the activation energy in joules per mole, e is the constant 2.7183, and A is a constant called the frequency factor, which is related to the frequency of collisions and the orientation of the reacting molecules.
frequency factor A
+what does increase probability result in
reflects how well the reaction conditions favor properly oriented collisions between reactant molecules. An increased probability of effectively oriented collisions results in larger values for A and faster reaction rates.
The exponential term, e−Ea/RT,
describes the effect of activation energy on reaction rate
A lower activation energy results in a
greater fraction of adequately energized molecules and a faster reaction.
The exponential term also describes the effect of temperature on reaction rate….How?
A higher temperature represents a correspondingly greater fraction of molecules possessing sufficient energy (RT) to overcome the activation barrier (Ea)
Large value for Rate constant equals……
rate…
This yields a greater value for the rate constant and a correspondingly faster reaction rate.
A convenient approach for determining Ea for a reaction involves
*verbal word no number/equations
the measurement of k at two or more different temperatures and using an alternate version of the Arrhenius equation that takes the form of a linear equation
What is the linear form of the arrhenius equation?
+what does each mean? +what is the x and y axis
A plot of ln k versus 1/T is linear with a slope equal to -Ea/R and a y-intercept equal to ln A.
Two mathmatical/graphical rearrangement convenient approach for determining Ea for a reaction involves (2)
- graph the lnK vs 1/T graph and find slope and make it equal to -Ea/R
- point slope formula : lnK2-lnK1=-Ea/R(1/T2-1/T1)
ln (K1/K2)=Ea/R (1/T2-1/T1)
Reaction mechanism/reaction path (2)
+ex
A reaction mechanism is the sequence of elementary steps by which a chemical reaction occurs.
ex: ozone decomposition
Elementary steps
they occur……. and must…..
each steps in a reaction mechanism
These elementary reactions occur precisely as represented in the step equations, and they must sum to yield the balanced chemical equation representing the overall reaction
Intermediates
species produced in one step and consumed in a subsequent step
rate law for an elementary reaction may be
derived directly from the balanced chemical equation describing the reaction
2A + B → products
is rate = k[A]²[B].
rate-determining step
What does it limit +what does it determine?
The slowest step in a reaction mechanism
The rate-determining step limits the overall rate and therefore determines the rate law for the overall reaction.
molecularity
number of reactant species
For ex: molecularity of 1
unimolecular reaction+ex
involves the reaction of a single reactant species to produce one or more molecules of product:
bimolecular reaction
+ what are the two types?
involves two reactant species
termolecular reaction+ex
+Why are they uncommon?
the simultaneous collision of three atoms, molecules, or ions. Termolecular elementary reactions are uncommon because the probability of three particles colliding simultaneously is less than one one-thousandth of the probability of two particles colliding.
Rate limiting step
+what it does
The slowest step of the reaction that will limit the rate at which the overall reaction occurs
a reversible reaction is at equilibrium when
the rates of the forward and reverse processes are equal
How do you find the concentration of intermediates
catalyst
+how do they do this (2)
a substance that can increase the reaction rate without being consumed in the reaction
by providing an alternative reaction mechanism with a lower activation energy+provide a reaction path whose rate determining step is faster (lower Ea).
Homogenous catalyst+ states+one important thing about it
presennt int the same phase as the reactants, interacts with the reactants to form an intermediate substance which then decomposes or reacts with another reactant in one or more steps to regenerate the original catalyst and form product.
+participates in chemical reaction but is never consumed
heterogenous catalyst
+process of how it works
a catalyst that is present in a different phase (usually solid) than the reactants. Generally function by furnishing an active surface upon which a reaction can occur.
-gets absorbed andthe bonds can get weakened and go thru reactions. In the end it gets desorped.
integrated rate law about half life time rate between the diff order
no math or anything just decrease or increase
0th order- half life time decreases
1st order- half life time remain costant
2nd order- half life time increases
how to solve for A
Point slope form of arrhenius to find EA and sub back to arrhenius orginal to find A
how are catalyst shown in a chemical equation?
above the arrow
