chemical kinetics 2

Question 1

what is an elementary reaction

Answer 1

reaction takes place in a single step

Question 2

what is a complex reaction

Answer 2

takes place by a set of elementary reactions (a mechanism)

Question 3

define rate determining step

Answer 3

the slowest stage in a reaction and is specified by the overall rate equation for the reaction

Question 4

how many species are in the rate determining step of an SN1 mechanism

Answer 4

1 species

Question 5

what are the orders in an SN1 reaction

Answer 5

1st order with respect to the organic molecule
0 order with respect to the nucleophile

Question 6

how many species are in the rate determining step of an SN2 mechanism

Answer 6

2 species

Question 7

what are the orders in an SN2 reaction

Answer 7

1st order with respect to both the organic molecule and the nucleophile

Question 8

in an exothermic enthalpy level diagram what is happening at the upwards part of the curve

Answer 8

bonds are breaking (energy taken in)

Question 9

in an exothermic enthalpy level diagram what is happening at the downwards part of the curve

Answer 9

bonds are being formed (energy released)

Question 10

define a catalyst

Answer 10

substance increases the rate of reaction by providing an alternative route or mechanism for a reaction with a lower activation energy

Question 11

what is a homogenous catalyst

Answer 11

catalyst that is in the same physical state as the reactants

Question 12

how does a homogenous catalyst work

Answer 12

reacts with one of the reactants to form an intermediate or activated complex which then reacts with the other reagent to reform the catalyst.

Question 13

what is a heterogenous catalyst

Answer 13

catalyst that is in a different physical state to the reactants (normally catalyst is solid and reactants are gases)

Question 14

how does a heterogenous catalyst work

Answer 14

solid catalyst has active sites which adsorb the gas molecules onto the surface
weakens the bonds
brings them together so they are more likely to react
product molecules released from the surface

Question 15

what three things do all catalysts have in common

Answer 15

• small amount required
• speed up reaction
• reformed at the end

Question 16

what is the Arrhenius equation with logs taken of both sides (ln)

Answer 16

ln k = ln A - Ea/RT

Question 17

what is k

Answer 17

rate constant

Question 18

what is A

Answer 18

Arrhenius constant

Question 19

what is Ea

Answer 19

activation energy

Question 20

what is R

Answer 20

gas constant 8.31

Question 21

what is T

Answer 21

temperature (K)

Question 22

what will the gradient be equal to (in the Arrhenius equation)

Answer 22

• Ea/R