Chem Exam II
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When determining and using initial rate laws there is
- -require experiemntal data
- -you are able to calculate reaction orders and calculate the value of the rate law
The integrate rate law does what?
-relates concentration to time
First order reaction rate law?
First order integrated rate law?
ln[A]t=-kt+ln[A]o as a linear equation
Time require to concentration of the reactiant to be reduced by one half its original concentration.
First order reaction half life equation?
- -for first order reactions the half-life is independant of the initial concentration
Second order reaction rate law?
Second order integrated rate law
1/[A]t=kt-1/[A]o as a linear equation
Second order reaction half-life equation?
- in the second order reation t1/2 depends on the intitial concentration.
If the temperature increases...
- Rate increases and
- k increases
To react, reactants must encounter eachother
If we increase the number of successful collisions you...
increase the rate
If you increase the reactant concentration....
you increase the number of collisions
Succesful collisions require:
- 1. collision must have sufficient energy
- 2. collision must have reactants in the proper orientation
Activation enegy is?
Energy barrier between the reactants and the products.
The transition state is
- short lived
- where the intermediate is created and destroyed between the reactants and products
- also called the activated complex
What determines if the reactnat have sufficient E to form the transistion state
- Energy (K.E.) of the reactant relative to the activation energy
- -increase speed of K.E.
- - lower the size of the barrier
Frequency equation is
If the frequency increases two things have happened
- the temperature as been increased
- the activation energy has decreased
- not all collisions with the K.E. higher than the Ea with result in a trantisition state formation.
- Bad collisions are caused from what and how the molecule is made.
Arrhenius equation is
A is the frequency factor and it is
- specific to each reaction
- depends on reactant geometry
- is independant of temperature
Uses of Arrhenius Equation
- Graphical determination of Ea lnk=(-Ea/R)(1/T)+lnA
- Determining k at various temperatures ln(k1/k2)=(Ea/R)(1/T2-1/T1)
- When solving for either k make sure it is in the k1 position
Reaction Mechanisms: Elementary steps
- describe the actual interactions between reactants at the molecular level
- descirve overall reactions as a series of steps; elementary steps: describe an actual collision
- explains rate laws
classification of elementary steps based on the number of reactnatn in the collision
Molecularity and Rate law
for an elementary step; molecularity determines the rate law for one step at a time
Molecularity determines the reaction order unimolecular rate law is
Molecularity determines the reaction order bimolecular rate law is
What is the rate determining step?
- a specal step in a mechanism
- slowest step in a mechanism
- determines the rate of the overal reaction
The rate law for the slowest step is what?
- the rate law for the overall reaction
- if the reaction occurs in one step the rate law correstongd to the overall reaction
Determining reaction mechanisms by four steps
- 1. based on experiemtnally determined rate law
- 2. mechanisms consist only of elementary steps- plausible collisions
- 3. one steop is rate determining-determines the overall rate law
- 4. The sum of steps=the overall reaction
Hints about reaction mechanisms
- mechanisms tent to occur in a minimal amount of steps
- reactions with a low overall reaction order (1 or 2) the initial step is usually the slowest
- reactions with a fast initial step often have higher (3) overall reaction orders
- reaction intermediates are usually in the slow reaction step(s)
a substance that decreases Ea, increases A in the Arrhenius equation
Homogenous catalyst is?
the catalyst and reactants are in the same phase
heterogenous catalyst is?
reactants and catalyst are in different phases
A catalyst is a reaction does what to the mechanism?
- lowers Ea by changing the transition state
- changes the reaction mechanism
- forms lower energy transition state
Heterogenous cataysis usually happens by surface catalyzing
- 1. adsorption: binding at the surface)
- 2. migration: of the adsorbed reactants
- 3. reaction at surface
- 4. desorption: products are relaeased from binding at catalyst surface
speed up a reaction
Protein structures based off of primary structure and secondary and teritary structure the shape dictates the function and activity of the protein
- primary structure-amino acid sequence
- secondary and tertiary structure- define the overall shape of the protein, maintained by the amino acid interactions
Enzyme mechanism process is a lock and key model
- 1. reacnant substrate bind to the enzyme at the active sight
- 2. forms enzyme sybstrate complez
- 3. products are released
Enzyme activity can be disruped by enzyme inhibitors by
- 1. binding to the active site
- 2. distoring the enzyme structure
what is Dynamic equilibrium?
- when forard and reverse reactions both occur at the same rate
- both reactants and products are presents in a constant ratio but seldom equal amounts
The product reaction ratio depends on
- theormodynamics of the reaction
- reaction conditions: temperature influence and pressure influence
establishing equilibrium means that
systems shift form initial conditions to establish the equilibrium ratio of the products to reactnat set by the reaction theromodynamics and the reactions conditions
equilibrium of gases is Kp
The relationship equation between Kc and Kp
Kp=Kc(RT)change in n
evaluating equilibrium constants
all k's are rations of prod/reactant
if product is >reactant and if reactant is > product
where does the equilibrium lie?
- Product > reactant it lies to the right
- reactant > product it lies to the left
Heterogenous equilibrium when reactants and products are in multiple phases what phases aren't in k expressions?
solids and liquids
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