Exam 4 Flashcards
Elementary reactions
a chemical rxn that only has one single transition state
reaction mechanism
the step by step sequence of a simple reaction by which an overall reaction occurs; sequence of elementary steps to ultimately form the rxn products
Unimolecular Elementary reaction
rearrangement of a single reactant molecule to produce 1 or more products
-A -> products
-rate =k [A]
Bimolecular Elementary reaction
the collision and reaction of 2 molecules/atoms in an elementary reaction
- A+B-> products OR A+A-> products
-rate =k [A][B] OR rate=k[A]^2
What effect does the conc of reactant have on number of collisions?
the number of collisions double as the conc of reactants double
rate= k[A]^2 double the collisions of rate= k[A]
Trimolecular elementary reaction
involves the simultaneous collision of 3 atom/molecules (low probability of occurrence)
Multistep reaction
reaction with 2 or more elementary steps
ex. O3 -> O2 + O ; O3 + O -> O2 + O2
reaction intermediate
atom or molecule that is a product in one reaction and a reactant in another
ex. O3 -> O2 + O ; O3 + O -> O2 + O2
reaction intermediate: O
Exergonic
G (products) < G (reactants);
decrease in G -> max useful work
Endergonic
G (products) > G (reactants);
increase in G -> max useful work
coupled reactions
reactions that occur simultaneously w/ a means of exchanging energy between them
ex. endergonic(thermodynamically unfavorable) and exergonic reactions coupled together, exergonic rxn energy drive overall reaction (slightly negative delta G overall)
Identifying a Catalyst
increases rate of rxn by providing an alternate pathway with a lower Ea
*normally more steps in mechanism
*involved in reaction but not consumed in rxn
What 2 factors cause a change in rate
Collision frequency and reaction energy
Units of k for 0-3 order rxn
0: m/s
1: s^-1
2: m^-1 s^-1
3: m^-2 s^-1
Rate of reaction equ
Change in concentration over change in time
Average rate of reaction
Rate of reaction over time that is clearly measurable (slope of tan like of conc v time curve)
Instantaneous rate of reaction
Rate at a specific point in the reaction/ where the change in time is very very small
inital rate
instantaneous rate at time zero
aA +bB -> dD + eE conc calculations
-1/a delta [A] = -1/b delta [B] =
+1/d delta [D] = +1/e delta [E]
rate determining step
slowest elementary step of multistep reaction
* smaller rate constant; larger Ea
rate when RDS is the first step
rate= k [reactants]
rate when RDS is NOT the first step
use equ approximation to approximate conc of intermediates which are reactants for RDS
*reverse and forward rxn equal at equ. ; use algebra and substitution to approx. conc of intermediate
Homogeneous catalyst
present in the same phase as the reactants
What do you know about the rate law if its an elementary rxn?
the rxn orders are the same at the reaction stoich coefficients
