(yellow) chemical kinetics II Flashcards
(yellow) chemical kinetics II
why is SN1 called Sn1
only 1 species in the slow step.
what is the rate determing step
Rate determining
step The slowest stage in a reaction and is specified by the overall rate equation for the reaction.
if you double the concentration and the rate doubles what order is it
second
if you double the concentration and the rate quadrupels what order is it
secondary
write the rate equation , determing step , with a and b
rate = k [a][b]
draw out an SN1 reaction
https://www.sciencedirect.com/topics/chemistry/sn1-mechanism
why are primary carbocations less stable than tertiary carbocations
as tertiary carbo cations can donate more electrons to stabalise the carbocation
on a enthalpy level diagram what is that dip called between the two transitions states
and what is it in SN1
intermediate carbocation
when R-C+(R)-R
what are the two transition states and what is a transition state:
A transition state is simply an arrangement of atoms that the reaction must pass through and is located at the maximum in the energy profile , note that transition states are not real molecules, and hence cannot be isolated.
rate determing transition state
secondary transition state
what is a intermediates
Intermediates are, like products and reactants, found at the minima in the energy profile. They are ‘real’ molecules, usually short lived and highly reactive, however they do not have the fleeting existence of transition states and in some cases can be isolated.
Notice the two energy peaks, the reaction has an intermediate stage.
remeber arrows only have one head on enthaply diagrams
??? do more revition ???
draw out an mechanism for SN2
https://www.masterorganicchemistry.com/2012/07/04/the-sn2-mechanism/
how would a curve of T2 > T1 look like if T represents tempreature , incule activation area
T2 curve would be lower , shifted more to the right , more are in activation area
what is a catalyst
A Catalyst is defined as a substance which increases the rate of a chemical reaction. It provides an alternative route or mechanism for a reaction with a lower activation energy.
what are the two types of catalysts
Homogeneous catalysts
Heterogeneous catalysts
what is a homogenous catalust
Homogeneous catalysts – Here the catalyst is in the same physical state as the reactants. (usually liquids or in solution). The catalyst works by reacting with one of the reactants to form an intermediate or activated complex which then reacts with the other reagent to reform the catalyst. The catalyst often changes oxidation state in the process.
what is a heterogenous catalyst
Heterogeneous catalysts – Here the catalyst is in a different physical state to the reagents. Normally the catalyst is a solid and the reactants are gases.
The solid catalyst has active sites which adsorb the gas molecules onto the surface. This weakens the bonds in the reacting molecules and brings them together so they are more likely to collide and react. The product molecules are then released from the surface of the catalyst so that it can be reused.
- aDsorbtion - reactants bond weakly to the surface of the catalyst
- weak binding to surface and reaction therefor bonds are broken
- resorbstion - products leave surface of catalyst
common featurs of homogenous catalysts
There was rapid effervescence.
Small amount of catalyst, catalyst speeded up the reaction (a lot)
What three things do all catalysts have in common when considering their effect on a reaction?
Small amount of catalyst needed
Catalyst speeded up the reaction (a lot)
Catalyst reformed at the end of the reactio
what are the diffrences on a energy level diagram between a catalyst and a non catalyst
non-catalyst : has one big activation energy and one large curved line curved down or up
catalyst : has a smaller activation energy , also has an intermidiate and two curved lines down or up
Explain why adding a catalyst increase the rate of a reaction using the collision theory model
Without a catalyst the area to the right of the Ea under the curve is small i.e. few molecules have KE ≥ Ea
Addition of a catalyst lowers the Ea to a new Eacat, now a much greater proportion of molecules have KE ≥ Eacat and so have enough energy to react.
write the arrhenius equation and how would you rearange it to fit into a y=mx+c graph
K=Ae^-Ea/RT
k - rate constant
A - arrhenius coinstant
e - mathmatical quantaty
R - gas constant
T - kelvin
Ea - activation energy
lnK = lnA - Ea/R x 1/T
y = c - m x
how would you find actication energy from this equation K=Ae^-Ea/RT
ln K on y axis and 1/T on x
times value of gradient by RT and then you have Ea
just memorise this
2MnO4- + 16H+ + 5C2O4 2- —-> 2Mn2+ + 8H20 + 10CO2
2Mn2+ is an auto catalyst
autocatalytic if one of the reaction products is also a catalyst for the same reaction. Many forms of autocatalysis are recognized
