Rate Law

rate law expression of zero order

R = K

rate law expression of first order

R = K[A]

rate law expression of 2nd order

R = K[A]^2

integrated rate eq. of zero order

[A]t = [A]0 - kt

integrated rate eq. of first order

ln ([A]0/[A]t) = kt

integrated rate eq. of 2nd order

1/[A]t - 1/[A]0 = kt

half life equation of zero order

[A]0/2k

half life equation of 1st order

ln2/k or .693/k

half life equation of 2nd order

1/k[A]0

plot that gives straight line for zero order rxn

[A] vs. t (slope is negative)

plot that gives straight line for 1st order rxn

ln[A] vs. t (slope is negative)

plot that gives straight line for 2nd order reaction, what is the slope

1/[A] vs. t (slope is positive)

slope of the line for zero order reaction

-k

slope of the line for 1st order reaction

-k

slope of the line for 2nd order reaction

k

k units for zero order

conc/time

k units for 1st order

/time

k units for 2nd order

/conc*time

all radioactive decay is what order

1st order

rate law expression

R = k[A]^m

when the [A] doubles how does the rate change for the reaction if it was zero, 1st, or second

zero: rate remains unchanged. first: rate doubles. second: rate quadruples

rate

how fast reactants are used up or products are formed, look at in (change in observed property)/(change in time)

rate expressed for reactants vs products

(note: c = product, a = reactant) rate = delta[C]/delta t = -delta[A]/delta t

create a math expression for this reaction in terms of A. 2A + B --> C. What does this mean

rate = -delta[A]/(2*delta t). Means that A is decreasing two times faster than the formation of C and decreasing twice as fast as B.

what are the units of rate

concentration/time

why is the initial rate the fastest

greatest change in time due to collision theory, that there are more reactants to react with

collision theory

process by which most chemical reactions are thought to occur. particles must collide w/ sufficient E and correct orientation in order for rxn to continue to products.

what gives you the instantaneous rate

plot the [ ] vs time and take tangent to curve at desired point

rate depends on what 4 factors

1. nature of reactant 2.concentration of reactant 3. temperature 4.catalysts

how does nature of reactant affect rxn rates

chemical identity, physical state (the more surface area of a solid or liquid will increase the rxn rate), reactions between ions (no bonds to break)

how does concentration of reactants affect rxn rates

rate law (first, second, zero order)

how does temperature affect rxn rates

collision theory (reactants moving faster) and integrated rate law (for every 10 degrees rxn rate doubles because molecules move faster and collide more often)

how does catalyst affect rxn rates

(both heterogeneous and homogeneous) catalyst lower the activation energy hill and participates in rxn yet it is fully recoverable after the rxn, can also speed up a reaction

reaction mechanism

series of steps by which a reaction is thought to occur; how many steps it takes a rxn to occur

rate is always...

positive

the rxn mechanism is comparable to what

comparable to the route taken by the rxn

the chemical equation specifies what

the origin and destination, but not the route traveled

elementary steps or elementary reactions

series of simple reactions

overall rxn represents what 2 things

represent the progress of reaction at a molecular level(series of elementary steps, which make up the reaction mechanism), and Hess's Law.

hess's law (two things)

the sum of elementary steps = overall rxn. The rxn goes only as fast as the slowest step

what does it mean if a rxn is single step (plus example)

the coefficients of reactants are the orders. Occurs in single step so... 2A + B --> C overall 3rd order rxn. R = k[A]^2[B]

bimolecular

2 different substances coming together

R = [NO]^2[Br], single elem. step, is this mechanism likely for this reaction

no, termolecular (3 different things coming together)

what is the rate determining step in a multi-elementary step rxn

the slowest step or the step with the highest Ea.

what must the rate determining step have

coefficients of the rate determining step must match the orders in the rate law. sum of steps must equal overall rxn

do rate laws include intermediates

no

what does it mean if the mechanism has an initial fast step

more difficult to derive rate law for mechanism if first step isn't the rate determining step as intermediate would then be a reactant in the rate determining step

if there is an equilibrium with an intermediate what do you do

substitute the intermediate

half life rxn for second order depends on what

concentration of [ ]0

integrated rate equation

allowed to find [ ] at particular time or amt of time that has elapsed

first order runs (with eq.)

those in wh/ rate depends on [reactants] raised to the first power. A --> products. Rate = -delta[A]/delta t. or k[A]

second order rxns

those wh/ rate depends on [reactants]^2. A --> product. rate = -delta[A]/delta t. or k[A]^2

half life rxn

time required the conc. of a reactant to decrease to half of its initial conc.

what does the collision theory explain

the effect of time and [ ] on rate of reaction explained

what two properties must a molecule possess in order to react according to the collision theory

1. must collide w/ proper orientation and sufficient energy. 2. anything wh/ increases # of collisions/unit time will also increase react rate

enthalpy is proportional to what

Potential energy

how does activation energy change

with change in temperature and use of catalyst

activation energy (what does it change with)

minimum energy required to raise the E of reactants to that of the activated complex, specific to rxn at a specific temperature

how is activation energy determined

determined experimentally