Corrosion 4

Question 1

term used to describe this reduction, denoted as ΔG

Answer 1

Reaction affinity

Question 2

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

Answer 2

Gibbs free energy change (ΔG)

Question 3

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

Answer 3

Gibbs free energy change (ΔG)

Question 4

said to be lost and a spontaneous reaction direction of the system is observed.

Answer 4

negative free energy

Question 5

change means that the transition indicates an energy increase, and it requires additional energy to be added to the system.

Answer 5

positive value of Gibbs free energy

Question 6

can be classified as a state function and is independent of the reaction path.

Answer 6

change in free energy

Question 7

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

Answer 7

electrical work (w)

Question 8

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

Answer 8

electromotive force (emf)

Question 9

higher tendency for the overall chemical reaction of the cell to proceed

Answer 9

higher value of E

Question 10

larger tendency to make the reaction proceed.

Answer 10

More negative value of ΔG

Question 11

value refers to a reaction that has no tendency to start at all.

Answer 11

positive ΔG°

Question 12

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

Answer 12

positive.

Question 13

ΔG = 0, ΔG > 0

Answer 13

reaction might not occur

Question 14

system is more likely to change in the other direction to that stated.

Answer 14

when ΔG > 0,

Question 15

activity coefficient

Answer 15

dissolved species

Question 16

fugacity coefficient

Answer 16

gaseous species

Question 17

the tendency of a material to corrode is not a direct measure of reaction rate.

Answer 17

true

Question 18

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

Answer 18

100 kPa and for solutes, the ideal concentration is 1 M (mol/L).

Question 19

equilibrium electrodes are also termed

Answer 19

half-cells

Question 20

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

Answer 20

standard half-cells

Question 21

an equation can be derived to determine the emf of a certain cell by virtue of the reactants and products’ concentration.

Answer 21

The Nernst Equation

Question 22

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

Answer 22

Nernst equation

Question 23

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

Answer 23

Electrode Kinetics

Question 24

The deviation from equilibrium potential is called

Answer 24

polarization

Question 25

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

Answer 25

Overvoltage

Question 26

electrochemical process that is controlled by the reaction sequence at the metal-electrolyte interface.

Answer 26

Activation Polarization

Question 27

usually is the controlling factor during corrosion in media containing a high concentration of active species.

Answer 27

Activation Polarization

Question 28

generally predominates when the concentration of the reducible species is small.

Answer 28

Concentration polarization

Question 29

• electrochemical reactions that are controlled by the diffusion in the electrolyte.

Answer 29

Concentration polarization

Question 30

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 30

Passivation

Question 31

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 31

Increased Corrosion

Question 32

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

Answer 32

Localized Corrosion

Question 33

amount of current (I) over a given area (A)
- The total charge that passes through the cell when N moles of the metal M react is Q.

Answer 33

CURRENT DENSITY

Question 34

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

Answer 34

tafel equation

Question 35

uniformly over the entire exposed surface.
- does not create a great concern, because the life of equipment can be accurately estimated on the basis of comparatively simple tests.

Answer 35

Uniform Corrosion

Question 36

Metal deterioration that happens in tight spaces where a stagnant liquid gets trapped.

Answer 36

Crevice Corrosion

Question 37

• A highly localized form of attack that eats away at the metal, creating small holes or cavities.

Answer 37

Pitting Corrosion

Question 38

Due to chemical composition difference at the grain boundaries from the bulk of the grain.

Question 39

two dissimilar metals with potential difference in a conductive solution.
- s a serious threat because it accelerates the deterioration of the less resistant metal.

Answer 39

Galvanic Corrosion

Question 40

Degradation that occurs when hydrogen penetrates the surface of a metal.

Answer 40

Hydrogen Damage