Chem Exam II

• -require experiemntal data
• -you are able to calculate reaction orders and calculate the value of the rate law

-relates concentration to time

rate=k[A]

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.

• t_1/2=0.693/k
• -for first order reactions the half-life is independant of the initial concentration

rate=k[A]²

1/[A]_t=kt-1/[A]_o as a linear equation

• t_1/2=1/[A]_ok
• in the second order reation t_1/2 depends on the intitial concentration.

• Rate increases and
• k increases

To react, reactants must encounter eachother

increase the rate

you increase the number of collisions

• 1. collision must have sufficient energy
• 2. collision must have reactants in the proper orientation

Energy barrier between the reactants and the products.

• short lived
• where the intermediate is created and destroyed between the reactants and products
• also called the activated complex

• Energy (K.E.) of the reactant relative to the activation energy
• -increase speed of K.E.
• - lower the size of the barrier

f=e^-E_a/RT

• the temperature as been increased
• the activation energy has decreased

• not all collisions with the K.E. higher than the E_a with result in a trantisition state formation.
• Bad collisions are caused from what and how the molecule is made.

k=Ae^-E_a/RT

• specific to each reaction
• depends on reactant geometry
• is independant of temperature

• Graphical determination of E_a lnk=(-E_a/R)(1/T)+lnA
• Determining k at various temperatures ln(k₁/k₂)=(E_a/R)(1/T₂-1/T₁)
• When solving for either k make sure it is in the k₁ position

• 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

for an elementary step; molecularity determines the rate law for one step at a time

rate=k[A]

• rate=k[A]²
• rate=k[A][B]

• a specal step in a mechanism
• slowest step in a mechanism
• determines the rate of the overal reaction

• the rate law for the overall reaction
• if the reaction occurs in one step the rate law correstongd to the overall reaction

• 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

• 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 E_a, increases A in the Arrhenius equation

the catalyst and reactants are in the same phase

reactants and catalyst are in different phases

• lowers E_a by changing the transition state
• changes the reaction mechanism
• forms lower energy transition state

• 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

amino acids

• primary structure-amino acid sequence
• secondary and tertiary structure- define the overall shape of the protein, maintained by the amino acid interactions

• 1. reacnant substrate bind to the enzyme at the active sight
• 2. forms enzyme sybstrate complez
• 3. products are released

• 1. binding to the active site
• 2. distoring the enzyme structure

• 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

• theormodynamics of the reaction
• reaction conditions: temperature influence and pressure influence

systems shift form initial conditions to establish the equilibrium ratio of the products to reactnat set by the reaction theromodynamics and the reactions conditions

k_c=[products]^coefficients/[reactants]^coefficients

k_p=(P_products)^coefficients/(P_reactants)^coefficients

K_p=K_c(RT)^{change in n}

• Product > reactant it lies to the right
• reactant > product it lies to the left

solids and liquids