# Chem Exam II

 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? rate=k[A] First order integrated rate law? ln[A]t=-kt+ln[A]o as a linear equation Half-life is? Time require to concentration of the reactiant to be reduced by one half its original concentration. First order reaction half life equation? t1/2=0.693/k-for first order reactions the half-life is independant of the initial concentration Second order reaction rate law? rate=k[A]2 Second order integrated rate law 1/[A]t=kt-1/[A]o as a linear equation Second order reaction half-life equation? t1/2=1/[A]okin the second order reation t1/2 depends on the intitial concentration. If the temperature increases... Rate increases and k increases Collision Theory 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 energy2. collision must have reactants in the proper orientation Activation enegy is? Energy barrier between the reactants and the products. Activation energy graph The transition state is short livedwhere the intermediate is created and destroyed between the reactants and productsalso 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 f=e-Ea/RT If the frequency increases two things have happened the temperature as been increasedthe activation energy has decreased Molecular Orientation 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 k=Ae-Ea/RT A is the frequency factor and it is specific to each reactiondepends on reactant geometry is independant of temperature Uses of Arrhenius Equation Graphical determination of Ea lnk=(-Ea/R)(1/T)+lnADetermining 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 leveldescirve overall reactions as a series of steps; elementary steps: describe an actual collisionexplains rate laws Molecularity 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 rate=k[A] Molecularity determines the reaction order bimolecular rate law is rate=k[A]2rate=k[A][B] What is the rate determining step? a specal step in a mechanismslowest step in a mechanismdetermines the rate of the overal reaction The rate law for the slowest step is what? the rate law for the overall reactionif 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 law2. mechanisms consist only of elementary steps- plausible collisions3. one steop is rate determining-determines the overall rate law4. The sum of steps=the overall reaction Hints about reaction mechanisms mechanisms tent to occur in a minimal amount of stepsreactions with a low overall reaction order (1 or 2) the initial step is usually the slowestreactions with a fast initial step often have higher (3) overall reaction ordersreaction intermediates are usually in the slow reaction step(s) Catalyst is? 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 statechanges the reaction mechanismforms lower energy transition state Heterogenous cataysis usually happens by surface catalyzing 1. adsorption: binding at the surface)2. migration: of the adsorbed reactants3. reaction at surface4. desorption: products are relaeased from binding at catalyst surface Enzymes speed up a reaction Proteins are amino acids 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 sequencesecondary 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 sight2. forms enzyme sybstrate complez3. products are released Enzyme activity can be disruped by enzyme inhibitors by 1. binding to the active site2. distoring the enzyme structure what is Dynamic equilibrium? when forard and reverse reactions both occur at the same rateboth reactants and products are presents in a constant ratio but seldom equal amounts The product reaction ratio depends on theormodynamics of the reactionreaction 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 Kcis what? kc=[products]coefficients/[reactants]coefficients equilibrium of gases is Kp kp=(Pproducts)coefficients/(Preactants)coefficients 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 rightreactant > 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 Authorgundrj ID69168 Card SetChem Exam II DescriptionRate and Equilibrium Updated2011-02-27T06:00:08Z Show Answers