01 Thermodynamics and Kinetics of Corrosion

Question 1

This determines whether the reaction is spontaneous, non-spontaneous or at equilibrium.

Answer 1

Gibbs free energy

Question 2

In this process, G decreases along with the _________________.

Answer 2

reaction time

Question 3

It can also be explained that during the reaction process, there is a driving voltage that is available. ________________ is the term used to describe this reduction, denoted as ΔG.

Answer 3

Reaction affinity

Question 4

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

Answer 4

change in Gibbs free energy (ΔG)

Question 5

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

Answer 5

change in Gibbs free energy (ΔG)

Question 6

When the change in free energy that accompanies a chemical the change of a system from one state to another is ______________, free energy is said to be lost and a spontaneous reaction direction of the system is observed.

Answer 6

negative

Question 7

Meanwhile, a _____________ value of Gibbs free energy change means that the transition indicates an energy increase, and it requires additional energy to be added to the system.

Answer 7

positive

Question 8

The change in free energy can be classified as a _________________ and is independent of the reaction path.

Answer 8

state function

Question 9

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

Answer 9

electrical work (W)

Question 10

Therefore, 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 as ________.

Answer 10

-nE

Question 11

w = ΔG = ________

Answer 11

-nFE

Question 12

For electrochemical reactions, the _________________ of the corrosion cells, which are crucial part of the corrosion process, can be used to express the tendency of a metal to corrode.

Answer 12

electromotive force (emf)

Question 13

A _____________ value of E for any type of cell means there is also a _____________ tendency for the overall chemical reaction of the cell to proceed, which is applicable to any type of cell.

Answer 13

higher; higher

Question 14

Under standard conditions, the ________________ is directly related to the standard cell potential difference across the cell.

Answer 14

standard free energy of the cell reaction, ΔG°

Question 15

ΔG° = ___________

Answer 15

-nFE°

Question 16

A more ____________ value of ΔG results in a ____________ tendency to make the reaction proceed.

Answer 16

negative; larger

Question 17

A _____________ ΔG° value refers to a reaction that has no tendency to start at all.

Answer 17

positive

Question 18

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

Answer 18

positive

Question 19

On the other hand, when the initial and final Gibbs free energy are __________, or when there is a ___________ driving voltage (ΔG > 0), there is enough reason to conclude that a reaction might not occur

Answer 19

same; negative

Question 20

When ΔG = 0, it is said that the reaction is said to be in an _____________ state.

Answer 20

equilibrium

Question 21

Meanwhile, when ΔG > 0, it is said that the system is more likely to change in the _____________ to that stated, unless the external energy of the system is affected by external forces.

Answer 21

other direction

Question 22

In the case of dissolved species, _____________ includes the effects of the system’s environment.

Answer 22

activity coefficient (γ)

Question 23

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

Answer 23

fugacity coefficient (Φ)

Question 24

Furthermore, the tendency of a material to corrode is not a direct measure of reaction rate. It is not always true that a large ______________ value of ΔG will result in a higher corrosion rate. However, a ______________ value of ΔG always indicates that a reaction will not proceed under certain conditions.

Answer 24

negative; positive

Question 25

The standard conditions for solid, liquid compounds, and even elements is the pure compound or element; in the case of gases, it is set at a pressure of _____________ and for solutes, the ideal concentration is _____________.

Answer 25

100 kPa; 1 M

Question 26

To calculate for the cell potentials, electrode potentials can be combined using algebraic methods. For instance, in the case of galvanic cells like _____________, the equation shown can be used.

Answer 26

Danielle cells

Question 27

In electrochemical or corrosion reactions, the accompanying change in free energy can be determined using knowledge regarding the _______________ of the reaction.

Answer 27

cell potential

Question 28

In this set-up, it is required that the system be in equilibrium. Therefore, in Figs. 5 and 6, the rates of ________________ and ________________ must be equal.

Answer 28

metal dissolution; deposition

Question 29

The equilibrium electrodes are also termed "____________". If these electrodes are maintained at equilibrium conditions, they are now called "____________".

Answer 29

half-cells; standard half-cells

Question 30

The positive terminal is connected to the Cu electrode (___________) and the negative terminal is connected to the Zn electrode (___________).

Answer 30

cathode; anode

Question 31

In this reaction, the change in Gibbs free energy, ΔG, is calculated from the difference between the ___________________ of products and reactants.

Answer 31

molal free energy

Question 32

However, if all the activities of reactants and products are equal to __________, the logarithm term becomes zero, and ΔG = ΔG°.

Answer 32

unity

Question 33

Since ΔG = −nFE , it follows that Δ G° = −nFE°, therefore, this expression shown is known as the _______________, which is used to determine the potential of a system wherein the reactants are not in unit activity.

Answer 33

Nernst equation

Question 34

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

Answer 34

Electrode Kinetics

Question 35

Galvanic Cell reduction: _______________ oxidation _____________

Answer 35

Cathode Anode

Question 36

reaction of gaining electrons: _________________

Answer 36

anodic/oxidation reaction

Question 37

The deviation from equilibrium potential is called ________________.

Answer 37

polarization

Question 38

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

Answer 38

Overvoltage

Question 39

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

Answer 39

Activation Polarization

Question 40

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

Answer 40

Concentration Polarization

Question 41

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

Answer 41

Activation Polarization

Question 42

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

Answer 42

Concentration Polarization

Question 43

Increasing the velocity or agitation of the corrosive medium will increase rate only if the cathodic process is controlled by ________________ polarization.

Answer 43

concentration

Question 44

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.

Answer 44

Passivation

Question 45

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.

Answer 45

Increased Corrosion

Question 46

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

Answer 46

Localized Corrosion

Question 47

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

Answer 47

current density (i)

Question 48

Q = _________

Answer 48

zFN

Question 49

i = ___/____

Answer 49

I/A

Question 50

This is the current density at equilibrium, or when the system isn't polarized/' overpotential'

Answer 50

exchange current density, (io)

Question 51

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

Answer 51

Tafel Equation

Question 52

n_diffusion = n_ion resistance = ____

Answer 52

zero

Question 53

Where there's no polarization, i_for is __________ to i_rev

Answer 53

equal

Question 54

When potential is higher at anodic site, i_net is equal to:

Answer 54

i_for - i_rev

Question 55

Simplifying the Tafel Equation gives the _____________.

Answer 55

Butler-Volmer Equation

Question 56

Change in entropy is evaluated at constant _____________.

Answer 56

pressure

Question 57

The process is facilitated by the presence of ______________, which allows for the flow of ions and electrons between the metal surface and the surrounding environment.

Answer 57

electrolyte

Question 58

The overall corrosion reaction can be described in terms of ______________ involving oxidation and reduction.

Answer 58

half-reactions

Question 59

The corrosion of metals occurs within a localized electrochemical cell known as a _______________.

Answer 59

corrosion cell

Question 60

A _________________ involves the spatial separation of anodic and cathodic areas on the metal surface leading to formation of corrosion sites.

Answer 60

corrosion cell

Question 61

The _____________ serves as a medium for ion transport.

Answer 61

electrolyte

Question 62

The standard electrode potential (E°) is the potential difference measured under standard conditions (1 M concentration, 1 atm pressure, and a temperature of 25°C) for a half-cell reaction relative to the _____________.

Answer 62

Standard Hydrogen Electrode (SHE)

Question 63

It is a historically important electrode. It is the halfcell in which hydrogen gas is bubbled over a platinum electrode immersed in a solution having a known concentration of hydrogen ions

Answer 63

Standard Hydrogen Electrode (SHE)

Question 64

Hydrogen equilibrium bears _________ value.

Answer 64

zero

Question 65

Those equilibria having higher standard potential than that of H+/H will be noble while the others having lower standard potential will be ___________ and corrode in acid solutions.

Answer 65

active

Question 66

In any electrochemical reaction, the most negative or active half-cell tends to be ___________, and the most positive or noble half-cell tends to be ___________.

Answer 66

oxidized; reduced

Question 67

Based on the value of Ecell, __________ in acid suffers corrosion.

Answer 67

Zn

Question 68

Relations between the energy and the potential of a cell to the concentrations of participating ions and other chemical species.

Answer 68

Nernst Equation

Question 69

This is a formula for:

Answer 69

Reaction Quotient

Question 70

Potential-pH diagrams, also called ______________, outline regions of active corrosion, oxides/hydroxides formation, and thermodynamic immunity for a metal.

Answer 70

Pourbaix diagrams

Question 71

If the oxides/hydroxides protect the underlying metal, then this region is called _______________.

Answer 71

passive region

Question 72

The _______________, also known as polarization in the context of corrosion kinetics, refers to the deviation in the potential (voltage) of an electrode from its equilibrium or rest potential during an electrochemical reaction.

Answer 72

Overpotential

Question 73

This is associated with the activation energy required to initiate the electrochemical reaction at the electrode surface. It represents the energy barrier that must be overcome for the reaction to proceed.

Answer 73

Activation Polarization

Question 74

____________ activation overpotential can contribute to increased corrosion resistance by reducing the rate at which the metal reacts with the corrosive environment.

Answer 74

High

Question 75

Activation polarization is due to ______________ that are an inherent part of the kinetics of all electrochemical reactions.

Answer 75

retarding factors

Question 76

The __________________ is the single most important variable that explains the large differences in the rate of hydrogen production on metallic surfaces. It is influenced by factors such as the nature of the reactants, the specific electrochemical system, and the presence of catalysts.

Answer 76

exchange current density

Question 77

________________ is often added to power cells such as the popular alkaline primary cells to stifle the thermodynamically favored production of gaseous hydrogen and prevent unpleasant incidents.

Answer 77

Mercury

Question 78

______________ batteries (car batteries) can provide power in a highly acidic environment in a relatively safe manner unless excessive charging currents are used.

Answer 78

Lead acid

Question 79

This type of overpotential arises from the variation in ion concentrations at the electrode interface.

Answer 79

Concentration polarization

Question 80

When a chemical species participating in a corrosion process is in short supply, the mass transfer of that species to the corroding surface can become __________________.

Answer 80

rate controlling

Question 81

Mass transport to a surface is governed by three forces, that is, _____________, _____________, and _____________.

Answer 81

diffusion, migration, and convection

Question 82

In mass transport, the ______________ term is negligible since it only affects charged ionic species while the ______________ force disappears in stagnant conditions.

Answer 82

migration; convection

Question 83

The flux of a species O to a surface from the bulk is described with _______________.

Answer 83

Fick's first law