Kinetics

first test semester 2- AP chemistry

activation energy

energy required in order for the action to occur

slow

when Ea is high, reaction occurs at a very ___ rate

activation energy

Ea

rate

= change in concentration/time interval

changes

usually rate ____ as the reaction proceeds

instantaneous rate

calculate the slope between 2 points on the concentration vs. time graph

relative rates

compare disappearance of reactants to each other and to the appearance of products

faster

the more moles of a substance, the ____ the rate is (greater number)

affects RR

nature of reactants

affects RR

chemical identity

affects RR

concentration of reactants

affects RR

temperature

slower

solids react ____ than liquids

chemical identity

bond energies can be important, and difficult to predict

collisions

more concentrated means more ___, so faster reaction

Temperature

faster movement (more KE) —> more collisions w energy to overcome Ea

affects RR

surface area of reactants

faster

greater surface area means ____ reaction

affects RR

adding an inert gas

inert gas

adding an ______ (N2 or noble) has no effect on reaction rate as long as pressure is not dramatically changed

affects RR

Catalysis

catalysis

substances that increase rate of reaction by lowering the activation energy

catalysts

• not consumed

• neither reactants are products

catalysts

offer different pathway

heterogenous catalyst

absorbs reactants so reaction can occur and then releases the product, in a different phase than reactants

homogenous catalyst

catalyst and reactants are in the same phase

rate laws

____ can only be determined from experimental data

zero order

if [A] is doubled, rate is constant

m = 0

first order

if [A] is doubled, rate doubles

m = 1

second order

if [A] is doubled, rate quadruples

m = 2

differential rate law

used when you have concentration and rate data

differential rate law

called the method of initial rates

differential rate law

no product buildup w this law

differential rate law

no reverse reactions w/ this law

integrated rate law

uses experimental concentrations and time data

0 order

constant rate, independent of [A]

0 order

graph of [A] vs time will be linear if its:

0 order

table will have a constant slope if its:

1st order

graph of ln[A] vs time is linear/constant slope

1st order

has a constant half life!!!

2nd order

graph of (1/[A]) vs time is linear (and a positive slope)

half life

t1/2

half life

the time it takes for a reactant to reach ½ of its concentration

t1/2

= 0.693/k

k

= constant

m

= exponent

swamping

use a large excess of one of the reactants such that its concentration does not change appreciable (noticeably) during the reaction

A

when you swamp with B, you measure ____ vs time and fire out its order

collision model

molecules must collide in order to react

essential

proper orientation of molecules is:

rate

anything that affects collisions, affects:

catalyst

often hold reactants in proper orientation

intermediate

substances produced in 1 step and used in a later step

mechanism

a representation of the series of bond making and bond breaking steps that occur during the conversion of reactants to products

mechanism

“how” the reaction occurs

slow

the rate determining step is the ___ step

slowest

the rate of overall reaction is limited by and equal to them combined rates of all elementary steps up to and including the _____ step, except intermediates

Catalyst

used to increase rate of reaction and it is regenerated

catalyst

should not appear in overall reaction

catalyst

may appear in mechanism but will be in a reactant and a product (so it cancels out)

peak

activated complex on a graph is represented by the:

activated complex

transition state is aka

bigger

the rate determining step/slow step is represented by a ____ hump on a graph

slow step

the rate determining step is the:

2 step

with a catalyst, the reaction is a _____ process

2 humps

2 step processes have:

intermediate

represented by a dip between humps

increasing pressure

____ of reactant gases means an increase in concentration, so more collisions

increasing temperature

_____ of reactants means that more molecules have the minimum activation energy

• also more collisions, higher KE

catalyst

adding a _____ lowers activation energy and helps with orientation

intermediates

produced in one step then used in another

catalysts

used up in one step and produced in a later step

integrated rate law

what you need to do to get a linear graph, possible to use swamping to determine order with respect to reactants

k

= absolute value of slope

activation energy

= minimum energy

initial rates

how does changing concentration affect rate (you are determining the exponent)