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CHEM191 MODULE 1 + 2 > MODULE 2 > Flashcards

MODULE 2 Flashcards

1
Q

What is kinetic energy

A

Energy of motion

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2
Q

What is potential energy

A

Energy of position - relative to other objects/force

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3
Q

What unit is used for energy

A

Joules (J)

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4
Q

How to go from J to kj

A

J divided by 1000

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5
Q

Energy is ……….. in exothermic reactions

A

Released

Negative change in enthalpy

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6
Q

Energy is …….. in endothermic reactions

A

Absorbed

Positive enthalpy change

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7
Q

A positive enthalpy change means the reaction is …….

A

Endothermic

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8
Q

A negative enthalpy change means the reaction is

A

Exothermic

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9
Q

How to work out change in enthalpy

A

Enthalpy of products - enthalpy of reactants

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10
Q

What is entropy

A

Measure of possible arrangements within a system

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11
Q

A high entropy would indicate

A

Greater amount of possible arrangements within a system, more disorder

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12
Q

A low entropy would indicate

A

Fewer possible arrangements within a system, more ordered

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13
Q

What is the spontaneous direction os entropy

A

Increasing entropy

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14
Q

Which state has the highest entropy

A

Gas

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15
Q

If a gas is forming from a solid is the entropy change likely to be positive or negative

A

Positive

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16
Q

Does fewer moles mean more or less possible arrangements

A

Fewer moles = less arrangements

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17
Q

If a reaction has fewer moles of products than reactants (all in the same phase) is it likely to have a negative or positive entropy change

A

likely to have negative entropy change

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18
Q

If the change in G is negative will the reaction be spontaneous

A

Yes

negative G = spontaneous
Positive G = Non spontaneous

Zero G = equilibrium

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19
Q

What can be said about the spontaneity of a reaction if change in H is + and change in S is -

A

The reaction can NEVER be spontaneous at any temperature

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20
Q

What can be said about the spontaneity of a reaction if the change in H is - and the change in s is +

A

The reaction WILL be spontaneous at all temperatures

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21
Q

If the change in H and S for a reaction have the same sign what can be said about the spontaneity of the reaction

A

The spontaneity will depend on temperature

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22
Q

If change in both H and S is positive when will the reaction be spontaneous

A

ONLY at high temperatures

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23
Q

If change in both H and S is negative when will the reaction be spontaneous

A

ONLY at low temperatures

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24
Q

What is a coupled reaction

A

When a spontaneous reaction (negative change in G) is used to drive a non spontaneous reaction (positive change in G) by coupling them together

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25
Q

Unit for rate of reaction

A

mol L-1 s-1

Conc divided by time

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26
Q

Factors affecting rate of reaction

A
  • chemical nature if reaction
  • physical states of reactants and products
  • concentration of reactants
  • temperature

Catalyst = increase reaction rate
Inhibitor = decrease reaction rate

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27
Q

general rate law for a reaction

A

Rate = k(A) power of x (B) power of y

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28
Q

What does x equal in rate law equation

A

Order in respect to A
x = 0,1,2 …..

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29
Q

What does y equal in the rate law equation

A

Order with respects to B
B = 0,1,2…..

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30
Q

What does x + y mean in rate law

A

Gives the overall order of the reaction

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31
Q

Do you take into account stoichiometry when writing a rate law

A

No ignore it, THIS IS THE ONLY TIME ITS IGNORED

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32
Q

The unit of k when overall order of reaction is 0
(x+y=0)

A

mol L-1 s-1

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33
Q

The units of k when overall order of reaction is 1
(X+y=1)

A

s-1

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34
Q

The units of k when the overall order of reaction is 2
(X+y=2)

A

L mol-1 s-1

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35
Q

The units for k when overall order of reaction is 3
(X+y=3)

A

L2 mol-2 s-1

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36
Q

How to calculate k (the rate constant)

A

K = initial rate divided by

A to power of x times B to power of y

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37
Q

How to find x in rate constant, using initial rates

A

Hold B constant,

measure initial rates for different values of A
- changing the concentration of A

38
Q

How to find y in the rate constant using the initial rates method

A

Hold A constant,

Measure initial rates for different values of B
- different concentrations of B

39
Q

Does rate constant k increase or decrease with temperature

A

Increase

40
Q

If the concentration of A doubles and there is no change to the initial rate what order will the reaction be

A

Order 0

41
Q

If the concentration of A doubles and the rate also doubles what order will it be

A

1

42
Q

If the concentration of A doubles and the rate increases by more than double

A

2nd order

43
Q

What is the concept half life

A

Time taken for reactant to reach half its initial value

At half life t = 1/2t

44
Q

What is an elementary step

A

Series of steps a reaction takes to complete an overall reaction

  • stoichiometry IS USED when writing rate laws for elementary steps - ONLY TIME for rate laws
45
Q

What is a reaction mechanism

A

Elementary steps describing an overall reaction

46
Q

What is a reaction intermediate

A

Species which play a role in the reaction but do not appear in the overall equation

  • created and used in the elementary steps
47
Q

What is a rate determining step

A

The slowest elementary step, that determines the reaction rate

48
Q

`if the first elementary step is rate determining how would you write a rate law

A

Use stoichiometry to write the rate law for that step

Rate = rate determining step = k1(……..)

49
Q

If the second elementary step is rate determining how would you write a rate law

A

Write the rate law using stoichiometry
- the rate law may contain intermediates = these must be removed

Write the equilibrium constant for first step

Rearrange equilibrium constant to equal the intermediate needing to be removed

Then substitute this rearranged equilibrium constant into the rate law in place of intermediate

50
Q

Which elementary step would show the greatest peak on energy profile graph ……… and why

A

The slowest elementary step as it requires the greatest amount of activation energy

51
Q

What is molecularity

A

The total number of species involved in a single collision leading to a reaction

52
Q

How to get from minutes to seconds

A

Times by 60

53
Q

How to get from minutes-1 to seconds-1

A

Divide by 60

54
Q

What is activation energy

A

The energy threshold needed to be overcome for a reactant to be converted into a product

55
Q

What is transition state

A

Where bonds are partly broken and partly formed

Where the reaction will either form products (effective collision) or return to reactants (ineffective collision)

56
Q

How does temperature impact reaction rate

A

It effects collision frequency and collision effectiveness

  • increase in temp = molecules move faster = more energy
57
Q

Oxidation means that electrons are …..

A

Lost, cation is formed

58
Q

Reduction means that electrons are ……

A

Gained

59
Q

When atoms exist as elements their oxidation number is …

A

0

60
Q

The oxidation number of a monoatomic ion is

A

The same charge as the ion

61
Q

Hydrogen in compounds has an oxidation number of …

A

+1

62
Q

Oxygen has an oxidation number of -2 in compounds expect which compound

A

Hydrogen peroxide (H202) - it has an oxidation number of -1 in this

63
Q

The sum of oxidation numbers in molecules always equals…

A

0

64
Q

The sum of oxidation numbers in polyatomic ions is

A

Equal to the charge of the charge of the ion

65
Q

What is an oxidising agent

A

The reactant that is causing oxidation

It itself is being reduced, but it is causing another species to lose electrons

66
Q

What is a reducing agent

A

The reactant that is causing reduction

It itself is being oxidised but it is causing another species to gain electrons

67
Q

The substance with the highest potential energy in spontaneous redox reactions will …..

A

Be reduced

68
Q

How to calculate potential difference of a reaction

A

Use the values given to you
Reduction process - oxidation process

69
Q

Will the potential energy difference always be positive or negative for a spontaneous reaction

A

It will always be positive

70
Q

If Eo cell is positive reduction will occur at the ….. electrode

A

Right hand side electrode

71
Q

If Eo cell is negative then reduction will occur at the …….. electrode

A

Left hand side electrode

72
Q

What does Eocell measure

A

How much each side wants to gain electrons

73
Q

How do you work out Eocell

A

Eo of right hand side - Eo of left hand side

74
Q

Reduction always occurs at the ……..ode

A

Cathode

75
Q

Oxidation always occurs at the ….ode

A

Anode

76
Q

How do you know if a reaction has a pH dependent reduction potential

A

If the reaction contains H+

77
Q

What is biological standard state

A

When all species are in standard conditions
1 mol L-1 except hydrogen

H+ has concentration of 1x10-7 - a realistic biological concentration

78
Q

An increase in Q means that E will ….

A

Decrease

79
Q

Change in G under standard conditions equals what at equilibrium

A

Zero

80
Q

What are the issues with chemical oxidants in biological environments

A

They are often toxic
Require a low pH
Also are un selective (cause anything to oxidise)

81
Q

Biological oxidants must themselves be able to be….

A

Reduced and then re-oxidised when they pass on electrons

82
Q

What is a transition metal complex

A

Compounds in which a transition metal has a number of ligands bonded to it

83
Q

What is a ligand

A

A molecule or ion which has one or more donor atoms that have a lone pair of electrons

84
Q

A ligand is a Lewis ………

A

Lewis base

85
Q

Common donor atoms in ligands are ….

A

Nitrogen and oxygen

86
Q

Transition metals are Lewis….. and will always be a …ion

A

Lewis acids and will always be a cation

87
Q

When ligands bond to transition metals they change the ….

A

Reduction potential of the transition ion

88
Q

If a very electronegative element is bonded to the outside of a cytochrome it will….. the reduction potential

A

Increase the reduction potential of the transition metal

89
Q

If a transition metal complex has strong electronegative elements bonded to the outside of it will the reduction potential of the transition metal be reduced or increased and why

A

The reduction potential will increase because the electronegative element will pull electron density away from the transition metal, making it want to gain more electrons

90
Q

How to work out the reduction potential, under standard conditions when given the pH

A

E(standard conditions) - 8.314 x temp / n x 96485 x In (1 / (1x10 to the power of negative ph) to the power of the number of hydrogens in the equation

CHEM191 MODULE 1 + 2 (2 decks)

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