It is not necessarily consistent with the valence (the ratio of the number of atoms combined).

The apparent charge of an atom of an element

Half reactions consist of different oxidation numbers of atoms of the same element, where oxygen The one with a higher chemical number is in the oxidation state, and the one with a lower oxidation number is in the reduced state.

When the medium or other substances in the solution participate in the half-reaction, it should also be written

write ionic equation

Write a half-reaction based on the redox couple

Balance half-reactions (especially O atoms) according to mass conservation and charge conservation

Determine the two half-reaction coefficients and combine the half-reactions

step

Re1 Ox2 == Ox1 Re2

(-) Zn(s)︱ZnSO4(c1) ||CuSO4 (c2) ︱Cu(s) ( )

Metal - metal ion electrode

Gas-Ion Electrode

Metal - Metal refractory salt electrode

Redox electrode or concentration electrode

A "double electric layer" is formed between the metal surface and the solution interface. That is, the electrode potential difference

When the electrode to be measured is in the standard state, the electrode potential is measured, but the absolute value of the electrode potential cannot be measured.

Standard hydrogen electrode: the electrode potential is set to 0

Calomel electrode: Hg2Cl2(s) 2e -== 2Hg(l) 2Cl -(aq), φ(Hg2Cl2/Hg)=0.2412 (saturated)

Silver chloride electrode: AgCl(s) e -==Ag(s) Cl-(aq), φ(AgCl/Ag)=0.2223 (1mol/L)

△rGm=-nFE

lnKθ = nFEθ/(RT) lgKθ = nEθ/0.05916 (when T＝298.15K)

ΔG < 0, E > 0, spontaneous (output useful work)

ΔG = 0, E = 0, equilibrium

ΔG > 0, E < 0 cannot proceed spontaneously

acidity

Precipitation formation (important and difficult points)

Complex formation

Weak electrolyte generation

The left is the negative electrode, which performs oxidation; the right is the positive electrode, which performs reduction.

“|” indicates the phase interface and there is a potential difference.

"||" means salt bridge. The solution is close to the salt bridge, which reduces the liquid junction potential to negligible

The temperature must be indicated, otherwise it means 298.15 K. The state of matter must be indicated, the pressure must be indicated for gases, and the concentration must be indicated for solutions.

Gas electrodes and redox electrodes should be written with conductive inert electrodes, usually platinum electrodes, written on the outside, with solids and gases close to the electrode plates.

Oxidation reaction ‖ Reduction reaction Low valence state │ High valence state ‖ High valence state │ Low valence state