SECTION E

Question 1

What is the rate of a rection?

Answer 1

“The rate at which reagents are used up and products are formed”

Question 2

How is the rate of a reaction defined in terms of the concentrations of both reagents and products?

Answer 2

Question 3

What is the rate law?

Answer 3

The rate law expresses the relationship between the rate of reaction and the concentrations of reactants.

Question 4

What is the order of reaction?

Answer 4

The exponent to which [reactants] are raised in the rate law. It is determined experimentally.

Question 5

What is k?

Answer 5

K is the rate constant for the reaction. It depends onlyontemperature(andthenatureofthereactants).

Question 6

What do the integrated rate laws allow us to calculate?

Answer 6

Concentrations of each component as a function of time.

Question 7

What is the integrated rate law for zero order reactions?

Answer 7

Question 8

What are the units of k for zero, first and second order reactions?

Answer 8

1. mole L-1 sec-1
2. sec-1
3. L mole-1 sec-1

Question 9

How can we best describe the rate of a zero order reaction?

Answer 9

• It remains constant with time;
• the concentration of [A] decreases linearly with time

Question 10

What is the integrated rate law for a first order reaction?

Answer 10

Question 11

For a first order reaction, which of the two following graphs is linear?

a) [A] vs. t
b) ln[A] vs. t

Answer 11

B

Question 12

What is the half life?

Answer 12

1/2 is the time required for the concentration of the reagent to drop to half its original value

Question 13

What is the half life for first order reactions?

Answer 13

For first order reactions, it is independent of concentration.

Question 14

What is the significance of k?

Answer 14

It is the rate consant. Also called the proportionality constant, it depends on t (Arrhenius relation) but is independent of concentrations, and tells us how fast the reaction goes.

Question 15

Radioactive decay follows ____ order kinetics.

Answer 15

First order

Question 16

Which equation(s) best describea radioactive decay?

Answer 16

Question 17

Give an equation for radioactive decay that includes the half life

Answer 17

Question 18

What is the integrated rate law for a second order reaction?

Answer 18

Question 19

What is the defining feature of the half life for a second order reaction?

Answer 19

It depends on [A]o

Question 20

If a plot of 1/[A] vs t is linear, what is the order of the reaction?

Answer 20

Second order.

Question 21

What are pseudo first order conditions and what are they used for?

Answer 21

They are used for experimental determination of the order of reaction:

A + B → products

Rate = k[A]a[B]b

 Need to isolate the variation in [A] so Keep [B] the same but let [B] >>[A]
[B] is effectively constant (pseudo-order conditions) (isolation)

 Run the reaction at several different [A]0. Plot [A] vs. time

 Determine initial rate for each curve (draw tangent).

 Note that if we take logs: log(Rate) = log(kobs) + alog[A]

Get straight line graph with slope equal to the order of the reaction.

 The ratio of any two rates will be in proportion to the ratio of initial concentrations to the power of a.

+ log(Rate) = log(kobs) + alog[A] —> as it the gradient of a graph of log(rate) vs. log[A]

Question 22

In general, is the order associated with the stoichiometry of the reaction?

Answer 22

Nope

Question 23

What does the order of a reaction reflect?

Answer 23

The underlying mechanism of the reaction

Question 24

The order of elementary (unimolecular, bimolecular) reactions is equal to the ____________.

Answer 24

Molecularity (number of molecules that come together to react in an elementary reaction)

Question 25

What is the rate determining step?

Answer 25

If a reaction proceeds by a series of steps then the rate constant, k, of the slowest step governs the rate of the reaction.

Question 26

The ______ \_\_\_\_\_\_\_\_ _________ can be used to infer reaction mechanisms.

Answer 26

Steady state approximation.

Question 27

What is the Arrhenius relation?

Answer 27

Question 28

What is the Arrhenius plot?

Answer 28

lnK vs. 1/T Gradient: -Ea/R Intercept: lnA

Question 29

What is the significance of A in the Arrhenius relation?

Answer 29

It is the pre exponential factor. It takes into account the total number of collisions occurring per second in the reaction + the orientation of the molecules in the collision, which is also important.

Question 30

Why do reactions depend on T?

Answer 30

Most reactions depend on collisions in order to occur. Molecules require a collision of a threshold (minimum) energy in order to occur. – Activation Energy, EA.

Question 31

What is catalysis?

Answer 31

Catalysis is the increase in the rate of a chemical reaction due to the participation of an additional substance called a catalyst. With a catalyst, reactions occur faster and with less energy. Because catalysts are not consumed, they are recycled. Often only tiny amounts are required.

Question 32

What is a catalyst?

Answer 32

A substance which takes part in a reaction and changes its rate but which can be recovered unchanged at the end of the reaction (at least in theory). A catalyst provides the reaction with a separate mechanism (pathway) which has a lower activation energy than the unassisted route.

Question 33

What is a homogeneous catalyst?

Answer 33

Catalyst is in the same phase as the reactants. Example: any enzyme

Question 34

What is a heterogeneous catalyst?

Answer 34

Catalyst is in a different phase as the reactants e.g. reactants are gases, catalyst is solid. They are materials with the capability of adsorbing molecules of gases or liquids onto their surfaces. Example: Pt catalyses CO + 1/2\*O2 -----\> CO2

Question 35

What is the M-M equation?

Answer 35

V: rate of reaction Vmax: limiting rate of reaction Km: [S] at which the enzyme is 50% saturated

Question 36

In M-M kinetics, how does the order of the reaction change as a function of [S]?

Answer 36

[S] \<\< Km: first order [S] \>\> Km: zero order

Question 37

What is the turnover number of an enzyme?

Answer 37

Kcat: it is defined as the maximum number of molecules of substrate that an enzyme can convert to product per catalytic site per unit of time. It informs about the efficiency of the catalyst, how many substrate molecules can be processed per mol of enzyme per unit of time.

Question 38

What is the catalytic efficiency of an enzyme?

Answer 38

Kcat/Km It gives an indication of how efficient the enzyme is. It cannot be greater than the limit imposed by diffusion control (diffusion-limited enzymes).

Question 39

What is the equation of the LB plot?

Answer 39

Question 40

What does a LB plot look like?

Answer 40

Question 41

What is the equation for the Eadie-Hofstee plot?

Answer 41

Tip: take M-M equation, cross-multiply and divide by [S]

Question 42

What does the EH plot look like?

Answer 42

Question 43

What type of inhibition is this?

Answer 43

Competitive

Question 44

What type of inhibition is this?

Answer 44

Non-competitive (Km unchanged, Vmax is decreased)