(yellow) chemical kinetics II

Question 1

why is SN1 called Sn1

Answer 1

only 1 species in the slow step.

Question 2

what is the rate determing step

Answer 2

Rate determining
step The slowest stage in a reaction and is specified by the overall rate equation for the reaction.

Question 3

if you double the concentration and the rate doubles what order is it

Answer 3

second

Question 4

if you double the concentration and the rate quadrupels what order is it

Answer 4

secondary

Question 5

write the rate equation , determing step , with a and b

Answer 5

rate = k [a][b]

Question 6

draw out an SN1 reaction

Answer 6

https://www.sciencedirect.com/topics/chemistry/sn1-mechanism

Question 7

why are primary carbocations less stable than tertiary carbocations

Answer 7

as tertiary carbo cations can donate more electrons to stabalise the carbocation

Question 8

on a enthalpy level diagram what is that dip called between the two transitions states

and what is it in SN1

Answer 8

intermediate carbocation

when R-C+(R)-R

Question 9

what are the two transition states and what is a transition state:

Answer 9

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

Question 10

what is a intermediates

Answer 10

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.

Question 11

remeber arrows only have one head on enthaply diagrams

Answer 11

??? do more revition ???

Question 12

draw out an mechanism for SN2

Answer 12

https://www.masterorganicchemistry.com/2012/07/04/the-sn2-mechanism/

Question 13

how would a curve of T2 > T1 look like if T represents tempreature , incule activation area

Answer 13

T2 curve would be lower , shifted more to the right , more are in activation area

Question 14

what is a catalyst

Answer 14

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.

Question 15

what are the two types of catalysts

Answer 15

Homogeneous catalysts

Heterogeneous catalysts

Question 16

what is a homogenous catalust

Answer 16

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.

Question 17

what is a heterogenous catalyst

Answer 17

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.

1. aDsorbtion - reactants bond weakly to the surface of the catalyst
2. weak binding to surface and reaction therefor bonds are broken
3. resorbstion - products leave surface of catalyst

Question 18

common featurs of homogenous catalysts

Answer 18

There was rapid effervescence.

Small amount of catalyst, catalyst speeded up the reaction (a lot)

Question 19

What three things do all catalysts have in common when considering their effect on a reaction?

Answer 19

Small amount of catalyst needed

Catalyst speeded up the reaction (a lot)

Catalyst reformed at the end of the reactio

Question 20

what are the diffrences on a energy level diagram between a catalyst and a non catalyst

Answer 20

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

Question 21

Explain why adding a catalyst increase the rate of a reaction using the collision theory model

Answer 21

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.

Question 22

write the arrhenius equation and how would you rearange it to fit into a y=mx+c graph

Answer 22

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

Question 23

how would you find actication energy from this equation K=Ae^-Ea/RT

Answer 23

ln K on y axis and 1/T on x

times value of gradient by RT and then you have Ea

Question 24

just memorise this

Answer 24

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