Redox Reactions: Understanding Electrode Potentials
Measurement of Energy in Redox Processes
The energy associated with a single redox process cannot be measured; only two processes together are measured. Taking the energy of the hydrogen electrode as a reference = 0 volts.
Electrode Potentials
A cell consisting of a type X electrode (cathode) versus a hydrogen electrode (anode).
The energy of redox processes taking place in solution is measured in volts, and it depends on the concentration.
Potentials given in the tables are measured at 1M of cations in the reaction.
The value of the potential of the oxidant must be greater than the reduction for the redox reaction to be spontaneous.
Effects of Concentration
The values of the potential depend on the concentration. The more concentrated this species is, the faster it will tend to fall and the greater the E. The problem is solved by the Nernst equation. If the oxidant or dissolved concentration is 0, it is taken as 1 in the equation.
Increasing E increases oxidizing power, a stronger oxidant, a weaker reducer, and vice versa.
Amphoteric Species
- Stable Amphoteric: The oxidizing potential is not greater than the reduction potential; then there is no reaction.
- Unstable Amphoteric: The amphoteric is reduced and oxidized with itself (dismutation). The amphoteric cannot exist in solution if it dismutes.
Influence of pH
When the oxidizer loses oxygen because the O2 reacts with the protons of the medium, the potential of the tables is taken at pH 0 and 1 M. If pH increases, E decreases, making the system more reducing.
Redox in Water
Normally used as a solvent, water intervenes in two redox reactions as an oxidant or reductant.
- An oxidizer that has a potential greater than 1.23 to 0.06 is not stable.
- A reducer that has a potential lower than -0.06 in acute non-stable pH.
Influence of Complex Formation
If a redox system forms a complex with the oxidant, the potential of it decreases by decreasing the concentration of the oxidant.
Dissolution of Metals
To dissolve a metal, it must first be oxidized. There are three types of metals:
- Those with a potential less than 0, H+/H2 is used.
- Metals with a potential between 0 and 1, NO3H/NO is used.
- Noble metals, aqua regia is used.
Formation of Precipitates
If a precipitate forms with the oxidizer, E decreases because it decreases the concentration of the oxidant.
Measurement of Energy in Redox Processes
The energy associated with a single redox process cannot be measured; only two processes together are measured. Taking the energy of the hydrogen electrode as a reference = 0 volts.
Electrode Potentials
A cell consisting of a type X electrode (cathode) versus a hydrogen electrode (anode).
The energy of redox processes taking place in solution is measured in volts, and it depends on the concentration.
Potentials given in the tables are measured at 1M of cations in the reaction.
The value of the potential of the oxidant must be greater than the reduction for the redox reaction to be spontaneous.
Effects of Concentration
The values of the potential depend on the concentration. The more concentrated this species is, the faster it will tend to fall and the greater the E. The problem is solved by the Nernst equation. If the oxidant or dissolved concentration is 0, it is taken as 1 in the equation.
Increasing E increases oxidizing power, a stronger oxidant, a weaker reducer, and vice versa.
Amphoteric Species
- Stable Amphoteric: The oxidizing potential is not greater than the reduction potential; then there is no reaction.
- Unstable Amphoteric: The amphoteric is reduced and oxidized with itself (dismutation). The amphoteric cannot exist in solution if it dismutes.
Influence of pH
When the oxidizer loses oxygen because the O2 reacts with the protons of the medium, the potential of the tables is taken at pH 0 and 1 M. If pH increases, E decreases, making the system more reducing.
Redox in Water
Normally used as a solvent, water intervenes in two redox reactions as an oxidant or reductant.
- An oxidizer that has a potential greater than 1.23 to 0.06 is not stable.
- A reducer that has a potential lower than -0.06 in acute non-stable pH.
Influence of Complex Formation
If a redox system forms a complex with the oxidant, the potential of it decreases by decreasing the concentration of the oxidant.
Dissolution of Metals
To dissolve a metal, it must first be oxidized. There are three types of metals:
- Those with a potential less than 0, H+/H2 is used.
- Metals with a potential between 0 and 1, NO3H/NO is used.
- Noble metals, aqua regia is used.
Formation of Precipitates
If a precipitate forms with the oxidizer, E decreases because it decreases the concentration of the oxidant.