Corrosion 4 Flashcards
term used to describe this reduction, denoted as ΔG
Reaction affinity
a quantitative measure of a chemical reaction’s tendency to start, which includes the reaction of a metallic material with its environment.
Gibbs free energy change (ΔG)
- a direct measure of the work capacity or the maximum electric energy possible that is available from a system.
Gibbs free energy change (ΔG)
said to be lost and a spontaneous reaction direction of the system is observed.
negative free energy
change means that the transition indicates an energy increase, and it requires additional energy to be added to the system.
positive value of Gibbs free energy
can be classified as a state function and is independent of the reaction path.
change in free energy
can be defined as a product of charges moved (Q) and the electrochemical potential (E) through which it is moved.
electrical work (w)
crucial part of the corrosion process, can be used to express the tendency of a metal to corrode.
electromotive force (emf)
higher tendency for the overall chemical reaction of the cell to proceed
higher value of E
larger tendency to make the reaction proceed.
More negative value of ΔG
value refers to a reaction that has no tendency to start at all.
positive ΔG°
For a reaction to take place, the driving voltage must be
positive.
ΔG = 0, ΔG > 0
reaction might not occur
system is more likely to change in the other direction to that stated.
when ΔG > 0,
activity coefficient
dissolved species
fugacity coefficient
gaseous species
the tendency of a material to corrode is not a direct measure of reaction rate.
true
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
100 kPa and for solutes, the ideal concentration is 1 M (mol/L).
equilibrium electrodes are also termed
half-cells
”. If these electrodes are maintained at equilibrium conditions, they are now called
standard half-cells
an equation can be derived to determine the emf of a certain cell by virtue of the reactants and products’ concentration.
The Nernst Equation
used to determine the potential of a system wherein the reactants are not in unit activity.
Nernst equation
study of reaction rates at the interface between an electrode and a liquid.
Electrode Kinetics
The deviation from equilibrium potential is called
polarization