chapter 11: chemical kinetics Flashcards
what is kinetics
concerned w/ the speed rates of rxns
what is rate
changes in quantity in a given period of time
what is thermodynamics
tells the direction and extent of the reaction
what is a state function
independent of the path
thermodynamics has nothing to do with
kinetics
how can you determine the rate of reactions
monitoring the change in concentration
- reactions slow down every time
what is the instantaneous rate
the slope of a line tangent to the curve at any point
what is the initial rate
the instantaneous rate, t= 0
what is a rate law
shows how the rate depends on the concentrations
what is k
the rate constant
how do you determine the exponents
determined by the experiment
what are the rate law exponents
0,1,2
what is the overall reaction order
the sum of the orders w/ respect to each reactant in the rate law
how do you write the rate
use the reactants k[A]^a[B]^b
what are the units of rate constant
M^-1,S^-1
what is zero order
changing conc. has no effect on the rate
first order
rate changes by the same factor as the conc( doubles the initial concentration doubles the rate)
what is second order
the rate changes by the square of the factor the concentration changes
- doubling the initial concentration quaduples the rate
what is another name for rate laws
differntial rate laws
- used to calculate reaction rates when given reactant conc.
what is integrated rate laws
used to calculate the amount of reactants left after a certain amount of time has passed
what is the first order reaction equation
ln[At] = -kt+ ln[A0] y = mx + b
what are some characteristics of zero reactions
-rate=k[A]^0\
- doesn’t depend on concentration
- 2^0 =1, 3^0 -1
- M^1t^-1
equation: -kt + [A0]
slope = -k
what can you use to find the order of a reaction depending on the exponent
M^1-n t^-1
what is half life t1/2
time required for one half of a reactant to react
[A] @ 1/2 is one half the original then [At] = 0.5[A0]
what is the first order reaction 1/2 life equation
- does not depend on the initial concentration
- 0.693/k = t/1/2
what is the second order reaction equation
1/[At] = kt + 1/[A0]
y = mx + b
what is the half-life equation for second-order reactions
1\k[A0] = t1/2
what is the equation for a zero order 1/2 life equation
[A0] /2k
when do zero order reactions most likely occur
when a substance such as a metal surface or enzyme is required for a reaction to occur
what is the collision model
accounts for the observed characteristics of reaction rates
- molecules need to collide to react
what are the 4 factors that affect rate
- concentrations of reactants
- physical state of reactants
- temperate
- structure and orientation of reacting particles
how concentrations of reactants affect rate
- increase in concentration = increase that the mlcls will collide = increase in rate
-reducing volume / increasing pressure on gas = concentration increase
phyisical state of reactants and rate
- reactants that are more homogenous the faster it will react
- reactants in diff. phases = limited area of contact
- limited area = reactions that involve solids proceed faster if the surface area of the solid is increased
temperature and rates
- higher temp = more KE = molecules will collide more often and w/ greater energy
- rate increases bc of temperature rising
structure and rates
- greater frequency of collisiosn = greater rate of reaction
for a collision to lead to a rxn what needs to occur
has to have enough energy to stretch bonds to form new bonds in other proper locations
what are effective collisions
collisions in which the 2 conditions are met (greater frequency + lead to reaction)
- increase in EFFECTIVE collision = faster rate
what is activation energy
- Svante Arrhenius
- energy that molecules possess in order to react
what is a reaction coordinate diagram
- very top of the hill is the transitions tate
- right = products
- left = reactants
what is the activated complex and activation energy barrier
- activated complex: species present at the transition state
- activation energy barrier= the energy gap between the reactants and the activated complex
difference in Ea of the forward vs. reverse
Ea is always higher for endothermic proc3sses
what is the arrhenius equation
ln k = -Ea/R(1/T) + Ln A
- T = temp in kelbin
- Ea = activatio energy
- R = 8.314 J/ mol k
A = frequency factor
what is a frequency factor
the likelihood that collisions would occur w/ proper orientation for reaction
what arrhenius equation is used to evauluate 2 or more temps
ln k1/k2= Ea/R(1/t2 - 1/T1)
what does a balanced equattion not tell us
how the reaction occurs
what is the reaction mechanism
the sequence of events that describes the actual process of how reactants turn into products
what is each step known as in a reaction mechanism
elementary reaction
what is an INTERMEDIATE
substance that is formed first as a product then consumed as a reactant
what is molecularity
the number of reactants molecules in an elementary step
what are the different molecularitys
- unimolecular = k[A]
- bimolecular = 2
- termolecular = 3
what happens in a mulistep process
one process will be slower than the others and this is the rate determining step
why is the slowest step the rate determining ste[
slowest step has the largest activation energy
what is a catalyst
a substance that changes the rate of a reaction w/out being permanently consumed
- consumed in an early step in the reactants and then produced in the products at a later step
what is a homogenous catalyst
present in the same phase as the reactant molecules
what is a heterogenous catalyst
present in a different phase than the reactant molecules
- catalyst can speed up a reaction by holding the reactants together and helping to break bonds
what is an enzyme
protein molecules that catalyze biological reactions
- active site: the place of the reaction
what is sibstrate and the lock and key model
- substrate: substances that undergo reactoin at the site
- lock and key model: enzymes are specific and they fit inside certain substrates
