Kinetics

Question 1

Chemical kinetics

Answer 1

The study of chemical reactions and the factors which affect them

Question 2

Rate

Answer 2

Is the change in conc per unit time

Question 3

Do the units for rate ever change and what are they?

Answer 3

No they do not change

mol L-1 s-1

Question 4

Rate law

Answer 4

Is the relationship between rate and concentration

rate α [concn]2

Question 5

Rate Law - 0 order

Answer 5

Rate independent of concentration

rate = constant

Question 6

Rate Law - 1 Order

Answer 6

Rate is proportional to the concentration of the reactant

Question 7

Activation energy

Answer 7

Ea is the energy required by the reactants to reach the transition state.

Ea in rate constant = Ae − Ea/RT

Question 8

Reactive intermediate

Answer 8

A substance that is produced in one step of a reaction mechanism and consumed in a subsequent step.

e.g. A + B → C; C + D → products [C is a reactive intermediate.]

Question 9

Catalyst

Answer 9

Substance that affects rate of reaction, but is unchanged at the end of the reaction.

e.g. enzymes, I − in decomposition of H2O2etc

Question 10

Rate constant

Answer 10

Proportionality constant (k) in rate equation.

e.g. 1st order, rate = k[concentration]

Question 11

Half life

Answer 11

time taken for concentration to fall to half its initial value.

e.g. For a 1st order reaction t½ = ln2/k

Question 12

Integrated rate law

Answer 12

relationship between concentration and time.

e.g. [A] = [A]0e-kt

Question 13

Homogeneous catalyst

Answer 13

catalyst in same phase of the reactants that affects the rate of reaction but is unchanged at the end of the reaction

(e.g. I -/H2O2).

Question 14

Heterogeneous catalyst

Answer 14

Substance, in a different phase from the reactants, that affects the rate of reaction but is unchanged at the end of the reaction.

e.g. many metals such as catalytic converters

Question 15

Elementary reaction

Answer 15

An elementary reaction is a single bond breaking and/or bond forming step passing through a single transition state

Question 16

S config for enantiomers

Answer 16

descending priority of three higher ranked anti-clockwise

Question 17

Which is the most stable carbocation? rank them in order

Answer 17

stability 3 ° >2 ° >1 ° .

Question 18

Which type of molecule would have highest bp?

Answer 18

A linear one
No branching, “strongest” intermolecular interactions.

Strongest intermolecular interactions (STATE WHAT THE BONDING IS)

Question 19

Why would a compound have lowest bp?

Answer 19

least polar; no possibility of intermolecular hydrogen bonding.

Question 20

Rate Law = Second Order

Answer 20

where rate α [concn]2

where the overall order in the rate law is two.

e.g. rate α [A][B] (1st order in each of A and B)

Question 21

In chromatography, which polar or nonpolar moves in alumina column?

Answer 21

Least polar - therefore least attraction to the polar stationary phase so moves most quickly with
the mobile phase

Question 22

What is a vinyl halide?

Answer 22

Halogen attached to sp2 carbon

Question 23

R enantiomer?

Answer 23

descending order of priority of three higher ranked substituents in a clockwise direction.

Question 24

Transition state

Answer 24

in an elementary reaction is the point of highest energy between reactants and products

Question 25

Arrhenius equation

Answer 25

Equation that describes how rate constants depend on temperature and activation energy.

Question 26

Rate determining step

Answer 26

The slowest step in a reaction mechanism is the rate determining step

Question 27

Aryl group

Answer 27

Halogen directly bonded to sp2 carbon of aromatic ring

Question 28

Diastereomers?

Answer 28

Configurational stereoisomers with a non mirror image relationship

Question 29

Constitutional isomers?

Answer 29

Same molecular formula, different atom to atom bonding sequence.

Question 30

Third order reaction

Answer 30

Where the overall reaction order in the rate law is 3

The rate is 3rd order in a single reactant or 2nd order in one and 1st order in another or 1st order in each of three reactants.

rate α [A]3 or

rate α [A]2[B] or rate α [A][B][C]

Question 31

Average rate

Answer 31

is the change in rate over a time interval.

change concentration/change t (SQUARE LOOKING THING ON CURVED GRAPH)

Question 32

Instantaneous rate

Answer 32

instantaneous rate is the rate at a specific point in time during the course of the reaction

Tangent gives instantaneous rate

Question 33

Reaction mechanism

Answer 33

is the collection of individual (elementary) steps required to go from reactant to product.

Question 34

Units of 0 order

Answer 34

mol L-1 s-1

Question 35

Units 1st order

Answer 35

s-1

Question 36

Units for 2nd order

Answer 36

L mol-1 s-1

Question 37

Units for 3rd order

Answer 37

L2 mol-2 s-1