Kinetics

Question 1

What does it mean to study reaction kinetics?

Answer 1

Focused on studying how fast a process is by measuring changes over time.

Question 2

What is a slow reaction compared to a fast reaction?

Answer 2

Slow - small change in [ ] overtime
Fast - large change in [ ] overtime

Question 3

Define reaction rate

Answer 3

The change in [ ] divided by the time interval which the change is observed

m = change in [ ] / t

Can be determined through method of initial rates

Question 4

How do we mathematically describe reaction rate?

Answer 4

Instantaneous Reaction Rate =
-d[reactant]/dt = +d[product]/dt

Question 5

Define mass balance

Answer 5

Change in concentration for each component related to its coefficients

Question 6

What does stoichiometry and mass balance help determine?

Answer 6

The rate of formation and the rate of consumption

Question 7

Define rate law

Answer 7

An expression for the instantaneous reaction rate in terms of instantaneous concentration of the species involved in a reaction.

Rate = k[A]m[B]n

Question 8

Define a rate constant

Answer 8

A proportionality factor in the rate law relating reagent concentrations to reaction rate

k
-change with temp
- unique in reactions
- Have different units

Question 9

What does the reaction order do?

Answer 9

Shows the exponential dependence on each regent on the rate of reaction
Ex: m and n

Overall order = sum of exponents

Question 10

How do you find the rate law?

Answer 10

It is experimentally determined, NOT through stoichiometric derivatives

Question 11

How do you perform the method of initial rates? What does this method do?

Answer 11

Compare initial concentrations to the observed reaction rate to find the orders of the reaction. This ONLY depends on the reactants.

Question 12

What do you use integrated rate laws for?

Answer 12

To describe how the [ ]’s change overtime

Ex: rate = 1/1 d[A]/dt

Question 13

In[A]t - ln[A]0 = - kt

What order is this integrated rate law?

Answer 13

First order

A -> B

Question 14

[A]t/[A]0 = e -kt

What order is this?

Answer 14

This is first order.
Just a algebraic manipulation that is given on the formula sheet

Question 15

ln[A]t = -kt + ln[A]0

How do you recognize/ plot this graphically?

Answer 15

Y = m x + b respectively

ln[A]t = y
-kt = m
ln[A]0 = b

X is y intercept

Question 16

1/ [A]t = kt + 1/[A]0

What order of integrated rate law is this?

Answer 16

A second order
Given on formula sheet

A + A -> B
2A -> B
A +B -> C

Question 17

In a reaction of 2A -> B, what formula should you use to determine the time it takes for [A] to reach a 0.32M if [A]0 = 1.6M?

Answer 17

1/[A]t - 1/[A] = kt

Question 18

How do you draw/recognize second order reactions graphically?

Answer 18

1/ [A]t = kt + 1/[A]0
y = mx + b

1/ [A]t = y
kt = m
1/[A]0 = b

Question 19

What is pseudo- first order conditions?

Answer 19

Increase the concentration of one of two components relative to to the other, so the concentration appears constant over the course of the reaction.

k’

Done in lab

Question 20

[A]t = -kt + [A]0

What order is this integrated rate law?

Answer 20

Zero order

A + B -> C

Question 21

How do you draw/recognize this graphically?

Answer 21

[A]t = -kt + [A]0
Y = m x + b

Question 22

What is the formula for a 0th order half life?

Answer 22

t1/2 = [A]0 /2k

Question 23

What is the formula for the First order half life?

Answer 23

t1/2 = ln2/k

Question 24

What is the formula for the second order half life?

Answer 24

t1/2 = 1/k[A]0

Question 25

How does t1/2 vary throughout the first, second, and third orders?

Answer 25

0th order - t1/2 gets shorter
1st order - t1/2 is constant
2nd order - t1/2 is longer

Question 26

Define the overall reaction

Answer 26

The balanced chemical equation. Accounts for all input and output NOT the intermediates

Question 27

Define reaction mechanism

Answer 27

The step by step process. Shows intermediates

Question 28

Define intermediates

Answer 28

Species that are produced and consumed during the reaction. Appear in the mechanism but not in the overall reaction

Question 29

Define catalyst

Answer 29

Are consumed and regenerated. Do not appear in overall reaction

Question 30

Define an elementary reaction

Answer 30

Transition state occurs in a single step

Question 31

Define molecularity

Answer 31

The number of reactant molecular entities

Question 32

What does it mean to be unimolecular ?

Answer 32

1 reactant molecule

Question 33

What does it mean to be bimolecular?

Answer 33

2 reactant molecules

Question 34

What does it mean to be termolecular?

Answer 34

3 reactant molecules (rare)

Question 35

What is a reaction coordinate diagrams?

Answer 35

Energy diagram describing the path one molecule of reactant follows as it reacts to become products.

Shows change in G 2x dagger (how fast)
and change in G naught (how far)

Question 36

Where is the transition state located on the reaction coordinate diagram?

Answer 36

At the highest energy point when going from reactants to products. Top of change in G 2x dagger.

Question 37

How do you tell which reaction is slower and which is faster based on a reaction coordinate diagram?

Answer 37

The larger the change in G 2x dagger is, the slower the reaction is