Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

CHEM1039 > Kinetics > Flashcards

Kinetics Flashcards

1
Q

Define thermodynamics

A

it tells us whether a reaction can proceed spontaneously but doesn’t inform us about the rate at which the reaction proceeds

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Whats kinetics?

A

it looks at how the enrgy is distributed as the reaction proceeds

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Information for kinetics can’t be gained theretically, why is this the case? how is information gained instead?

A

It has to be gained experimentally, as plugging information into equations doesn’t tell you anything about the kinetics of something

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

whats speed/ velocity?

A

the distance something has travelled in a given time

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Whats the rate of reaction?

A

the amount of material produced or consumed in a given time

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Label the key aspects on this energy profile

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Whats the difference between the reactants energy and products energy?

A

∆G

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Why are transition states so unstable?

A

due to their high energies

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Whats one of the main problems that arises when studying reaction rates?

A

the transition states and intermediates cannot usually be probed directly as they are very short lived

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Whats the thing we can only measure to calculate reaction rates?

A

we can only measure the concentration of the reactants and/or the products with time, and use this information to calculate the reaction rate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are the 2 key enzymes reaquired in this reaction?

What cofactor is useful for this reaction to occur also?

A

the cofactor, zinc, is needed for the enzyme to work as it helps to hold the enzyme, alcohol and NAD+ together in the correct position

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

why must acetaldehye be degraded quickly?

A

its toxic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

whats is rate defined as?

A

the change of the concentration of a species as a function of time

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

On a concentration-time graph, what does the gradient tell you?

d[reactant/product]/ dt

A

the rate at the particular point during the reaction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Many concentration-time relationships are non-linear what does this mean for the rate?

A

the rate will change as a function of time (the rate is not the same throughout the reaction)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are the two generalisations of the rate constant?

Write any equations that support these generalisations

A
  1. The rate usually decreases if the concentration of the reactants are decreased

d[products] / dt = K[A]X[B]Y

K= the rate constant

X and Y= the orders of the reaction

  1. The rate always increases with increasing temperature

K= A exp (-Ea / RT)

A and Ea can be treated as constants over small temperature ranges

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What are the 2 main reaction rate theories?

A
  1. collision theory
  2. transition state theory
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Whats meant by a simple reaction?

A

A reaction that occurs in a single step with no intermediates

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Whats the collision theory?

What it focusses on/ assumptions

A
  • this theory focusses on the molecular nature of the reaction and provides more insight into the behaviour of individual molecules
  • assumption of theory; the reactants and products must collide before the reaction occurs
  • they must collide with enought energy to overcome the activation energy barrier for the reaction
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

do spontaneous reactions have activation energy?

A

yes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is the rate of collision detemined by and how does this effect the rate of reaction?

A
  1. the concentration of products and reactants (more molecules increase the chance of collision)
  2. molecule size (bigger molecules have more chance of collision)
  3. speed (molecules moving faster are more likely to collide )
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Whats the equation for rate of collision?

A

rate of collision= πr2VR[A][B]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Whats the formula for rate and for K in the Collision theory law ?

A

Rate= k [A][B]

K= πr2VR exp (-Ea /RT)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is rate related to?

A

The reactants

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What are the units of rate?

A

moldm-3s-1

26
Q

Is the reaction rate constant K, a constant value? if not then what makes the value change?

A

It’ s not constant, it can vary depending on temperature, adding catalyst or changing the catalyst for example

27
Q

What does the order of a reaction tell us?

A

What happens in the rate determining step of a particular mechainsm

28
Q

Tell me the rate equation and units of K for the following types of reactions…

  1. A –> B order :0
  2. A –> B order: 1
  3. A –> B order: 2
  4. A + B –> C order: 2
A

A –> B order: 0

rate equation: K

units for K: mol dm-3 S-1

A –> B order: 1

rate equation: K[A]

units for K: S-1

A –> B order: 2

rate equation: K[A]2

units for K: mol-1 dm3 S-1

A + B –> C order: 2

rate equation: K [A][B]

units for K: mol-1 dm3 S-1

29
Q

what two methods can be used to determine the reaction order and rate constant?

How do you know/ decide what method to use?

A
  1. differential or direct method
  2. integration method

To decide what method to use, look at the system with several measurements and look at the concentration as a function of time

30
Q

What occurs in the direct method?

A
  1. A rate equation is produced for the reaction

A –> Products

  1. logs are taken from each side of the reaction

Log (rate) = log (k [A]a)

Log (rate)= alog[A] + log (k) (this is in form y= mx +c)

  1. this then puts the rate equation in the form y= mx + C

Y= log(rate)

M= a

X= log[A]

C= log(k)

  1. this can then be plotted on a graph and then extrapolated
31
Q

Draw rate-concentration graphs for zero, first and second order reactions

A
32
Q

Draw the conc-time graphs for zero, first and second order reactions

A
33
Q

Draw the rate of reaction- concentration graph for zero, first and second order reactions

A
34
Q

What is a first order reaction?

A

if doubling the concentration of a reactant has a double effect on the rate

35
Q

What is a second order reaction?

A

If doubling the concentration has a quadrupling effect on the rate

36
Q

Whats a third order reaction?

A

If doubling the concentration results in an eight-fold increase in rate

37
Q

whats K’ ?

A

Pseudo which is a first order rate constant

38
Q

Whats the integrated method?

A

the rate equation is made form the components of the reaction where they are then integrated and converted to a linear format in order to plot as a straight line of a graph

39
Q

What time of graph does the integration method lead to being able to produce?

A

A concentration- time plot

40
Q

For the following reaction write the rate equation with rate being written as a differential? and then the integrated rate equaiton your would get from this?

A –> products

A
41
Q

Write the following integrated rate equation in the form y=mx + c

A
42
Q

Write the following secord order reaction in linear form from the integrated rate equation…

A –> product

A

Rate = -d[A]/dt rate= k[A]2

put these two equations together and solve by integration

-d[A]/dt = k[A]2

1/[A]t – 1/[A]0 = kt (then put in form y=mx +c)

Y= 1/ [A]t

M= K

X= t

C= 1/[A]0

43
Q

Whats more accurate, the integrative method or the direct method and why?

A

The integrative method is more accurate than the direct method as the kinetic parameters are determined directly from a relationship between time and a function of the concentration

44
Q

The characteristic kinetic plot is just what you need to plot in order to get a straight line

Units of rate constant is variable

Rate is always the same

A

Learn this table off by heart

45
Q

Whats a chemical half life?

How is it denoted?

A

The time taken for a chemical species to fall to half its initial concentration

[A] –> [A] / 2

A half life is denoted as: t1/2

46
Q

What order reaction has a constant half life?

A

first order reactions have a constant half life

47
Q

When a reaction is faster, is there a shorter or longer half-life?

A

shorter

48
Q

What is the rate of reaction proportional to?

A

The rate constant, thus the larger the rate constant the shorter the half life

49
Q

How does the half life change with second order cases?

A

it gets longer and longer as time goes on as the reaction is slowing down

50
Q

Does this graph show a zero, first or second order reaction?

A

You can’t tell which one it is apart from the fact its not first as the half life isn’t constant

51
Q

Whats the half life eqaution for a second order reaction?

What does the equation suggest?

A

t1/2 = 1 / k[A]0

This inverse relationship suggests that as the initial concentration of reactant is increased, there is a higher probability of the two reactant molecules interacting to form a product

Also implies that since the half-life is longer when the concentration are low, species decaying according to second order kinetics may exist for longer amount of time if their initial concentration are small

52
Q

What are the steps in order to work out the kinetics of an unknown mechanism?

A
  1. start with the overall reaction
  2. guess some mechanism(s)
  3. derive corresponding rate laws (don’t need to derive as they’re given)
  4. compare with experimental data
  5. and repeat from step 3 as needed

if you dont get a straight line then something has gone wrong in the experiment or the mechanism is too complex (not zero, first or second)

53
Q

Whats the RDS?

A

The rate-determining step (RDS) is a single step in the mechanism which is much slower that there other steps

it can be thought of like a ‘bottle neck’ (nothing can happen until its happened, it influences the overall reaction)

54
Q

Look at SN1 and SN2 reactions and facts about their RDS

A
55
Q

Observations are made from experimental observations of what…

A

The rate laws

intermediates of the reaction

56
Q

Whats the collision theory formula and what does it tell us?

A

Rate= T [concentration]n

  • Rate is increasing dramatically
  • T: if rate is increasing dramatically, something on the other side of the equation must be increasing too. Must be the temperature
  • [Concentration]n: concentration is not changing much
57
Q

What are the two forms of Arrhenius equation in 1889 and what does each part stant for/ units

A

Form one: K = Ae(-Ea’/KBT)

Form two: K= Ae(-Ea/RT)

K= rate constant of the reaciton

A= pre-exponential factor (normalising factor)

E’a= the activation energy for the reaction (J)

Ea= the activation energy for the reaction (J mol-1)

T= temperature (K)

KB= Boltzmann’s constant

R= gas constant

58
Q

In Arrhenius’ equaiton there is an exponential factor, what does this mean for the results/effects?

A

its not linear and the effects are dramatic

59
Q

For the Arrhenius equation, complete these relationships…

if K increase T _____

If K decreases T _____

if K decreases the Ea _____

If K increases the Ea _____

A

if K increase T increases

If K decreases T decreases

if K decreases the Ea increases

If K increases the Ea decreases

60
Q

convert the following equation into a linear format…

K= Ae-Ea/RT

Write out in form y= mx+c

A

lnK = lnA - Ea / RT

y= ln K

m= -Ea/R

x= 1/ T

c= ln A (used to work out pre-exponential factor)

61
Q

How do you work out the Ea from a graph?

A

Ea= - gradient x R

62
Q

If T was raised by 10˚c, then the rate would double

What two ways can the arrhenius equation be written in order to form a general temperature between temperature and rate and write out the general relationship formula…

A

K1= Ae(-Ea/RT1)

K2= Ae(-Ea/RT2)

General relationship:

ln [K2/K1] = Ea/R {1/T2 - 1/T1}

NOTE; units of A are identical to units of K

Temperature is always in kelvin

Take the natural log of the K2/K1 ratio

CHEM1039 (11 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions