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Corrosion Engineering > Thermodynamics and Kinetics of Corrosion > Flashcards

Thermodynamics and Kinetics of Corrosion Flashcards

1
Q

the term used to describe this
reduction, denoted as ΔG (G decreases along with the reaction
time)

A

Reaction affinity

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2
Q

is a quantitative measure
of a chemical reaction’s tendency to start, which includes the reaction of a
metallic material with its environment.

A

Gibbs free energy change (ΔG)

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3
Q

It is also a direct measure of the work capacity or the maximum electric
energy possible that is available from a system

A

Gibbs free energy change (ΔG)

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4
Q

the change in free energy can be classified as a ____________function and is__________ of the reaction path.

A

state; independent

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5
Q

can be defined as a product of charges moved (Q) and the
electrochemical potential (E) through which it is moved

A

electrical work

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6
Q

in the
case of electrochemical cells and the charge is represented as 1 mol of
reactant in which n mol of electrons are transferred, the electrical work
done by the cell is quantified

A

-nE

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7
Q

which are crucial part of the corrosion process, can be
used to express the tendency of a metal to corrode

A

emf

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8
Q

for any type of cell means there is also a higher
tendency for the overall chemical reaction of the cell to proceed, which is
applicable to any type of cell

A

higher value of E

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9
Q

the standard free energy of the cell reaction,
ΔG° is directly related to the standard cell potential difference across the
cell, wherein

A

G= -nFE

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10
Q

____________ value of ΔG results in a larger tendency to make the reaction proceed

A

more negative

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11
Q

__________value of ΔG° (the reactants and products
are in their standard states) signifies an obvious likelihood for magnesium
to react with water and oxygen

A

large significant negative

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12
Q

For a reaction to take place, the driving voltage must be _

A

positive

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13
Q

On the other hand, when the initial and final Gibbs free energy are the
same (ΔG = 0) or when there is a negative driving voltage (ΔG > 0),
there is enough reason to conclude that a reaction might

A

not occur

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14
Q

when __________, it is said that the reaction is said to be in an equilibrium
state

A

ΔG = 0

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15
Q

When _____________, it is said that the system is more likely to change
in the other direction to that stated, unless the external energy of the
system is affected by external forces.

A

ΔG > 0

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16
Q

For dissolved species, ______________ which includes the effects of the system
’
s
environment

A

activity coefficient

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17
Q

In case of gaseous species, __________ includes the effects of the system’s environment

A

fugacity coefficient

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18
Q

Furthermore, the tendency of a material to corrode is ____________
of reaction rate

A

not a direct measure

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19
Q

It is not always true that a _____________ of ΔG will result in a higher corrosion rate

A

large negative value

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20
Q

a _______________
always indicates that a reaction will not proceed under certain
conditions

A

positive value of ΔG

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21
Q

The standard conditions for solid, liquid compounds, and even elements is

A

the pure compound or element

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22
Q

The standard conditions for gases is set at

A

P = 100kPa
C = 1M

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23
Q

The equilibrium electrodes are also termed

A

Half cells

24
Q

If these electrodes are maintained at
equilibrium conditions, they are now called

A

standard half-cells

25
Q

A potential difference of approximately ______________ V can be determined if a high-resistance voltmeter is connected between the Cu and Zn electrodes

A

1.10

26
Q

used to
determine the potential of a system wherein the reactants are not in unit
activity

A

Nernst equation

27
Q

The study of reaction rates at the interface between an
electrode and a liquid

A

Electrode kinetics

28
Q

an electrode at which a net oxidation process
occurs

A

anode

29
Q

an electrode at which a net reduction reaction
occurs

A

cathode

30
Q
  • synonymous with oxidation reaction (loses
    electron)
A

anodic reaction

31
Q

synonymous with reduction reaction
(gaining electron)

A

cathodic reaction

32
Q

The deviation from equilibrium
potential is called

A

polarization

33
Q

measurement of
magnitude of polarization with
respect to the equilibrium potential
of an electrode

A

overvoltage

34
Q

It refers to an electrochemical
process that is controlled by the
reaction sequence at the metalelectrolyte interface.

A

Activation Polarization

35
Q

usually is
the controlling factor during
corrosion in media containing a
high concentration of active
species (eg. concentrated acids)

A

Activation Polarization

36
Q

generally predominates when the
concentration of the reducible
species is small (eg. dilute acids,
aerated salt solutions).

A

Concentration Polarization

37
Q

Two types of polarization

A

Activation
Concentration

38
Q

It refers to electrochemical reactions that are controlled by
the diffusion in the electrolyte

A

Concentration Polarization

39
Q

Depending on what kind of polarization is controlling the
reduction reaction, __________ produce
different effects

A

environmental variables

40
Q

____________ the velocity or agitation of the corrosive
medium will increase rate only if the cathodic process is controlled by ____________

A

Increasing; concentration polarization.

41
Q

increase diffusion rate will __________ the effects of concentration polarization and hence _________reaction rate

A

decrease, increase

42
Q

polarization can lead to the formation of a
protective oxide layer on the metal’
s surface which acts as a
barrier, slowing down further corrosion

A

passivation

43
Q

polarization can also increase
corrosion rates by promoting more aggressive
electrochemical reactions. This can happen if conditions
favor the dissolution of the protective oxide layer

A

increased corrosion

44
Q

polarization gradients within the
metal surface can lead to the concentration of corrosive
agents in specific areas, accelerating corrosion rates locally

A

localized corrosion

45
Q

Effect of polarization in corrosion

A

Passivation
Increased corrosion
Localized corrosion

46
Q

Simply the amount of current (I) over a given area (A).

A

Current density

47
Q

The total charge that passes through
the cell when N moles of the metal M
react is Q

A

Q= zFN

48
Q

Current density , i and exchange current density, io, is estimated using ________

A

lab experiments

49
Q

Losses are considered in estimating current densities, including:

A

anodic and cathodic loss
loss due to ion resistance
diffusion loss

50
Q

a model for the current density of an
electrode when the only significant
limiting factor is activation

A

Tafel Equation

51
Q

Assumptions of tafel equation

A

(1) reaction is slow, therefore: (n diffusion = n ion resistance = 0)
(2) surface of a metal is at a potential E

52
Q

When Tafel equation is simplified, then:

A

Butler-Volmer Equation

53
Q

___________if only the first term is significant n>50mV since ia»ic

A

Corrosion (anodic polarization)

54
Q

Only the second term is significance if n<-50mV since ia«ic

A

Reduction reaction (cathodic polarization)

55
Q

ifor=irev if ________

A

no polarization

56
Q

inet=ifor-irev if _________

A

the potential is higher at anodic site

Corrosion Engineering (6 decks)

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