Question

Which of the following is not truc of electrode potentials? (1) They vary with concentration (2) They vary from clectrolyte to clectrolytc (3) They are indcpendent of temperature (4) They are dependent on the number of electrons involved in the reaction

Short answer

Statement (3) is not true.

Step-by-step solution

- Understanding Electrode Potentials

Electrode potentials, also known as standard electrode potentials, are measures of the individual potential of a reversible electrode at standard state, which includes a concentration of 1 mol/L, a pressure of 1 atm, and a temperature of 25°C (298 K).

- Evaluate Statement (1)

Electrode potentials vary with concentration because the potential is influenced by the concentration of ions in the electrolyte. This is a true statement.

- Evaluate Statement (2)

Electrode potentials vary from electrolyte to electrolyte as different electrolytes can have different ion concentrations, which affect the potential. This is also a true statement.

- Evaluate Statement (3)

Electrode potentials are not independent of temperature. Temperature affects the kinetic energy of particles and can change the potential of the electrode. This statement is false.

- Evaluate Statement (4)

Electrode potentials are dependent on the number of electrons involved in the reaction because the potential is influenced by the transfer of electrons during the reaction. This is a true statement.

- Conclusion

After evaluating all the statements, it is concluded that the statement 'They are independent of temperature' is not true for electrode potentials.

Key concepts

Concentration Effect on Electrode Potentials

Electrode potentials are influenced by the concentration of ions in the electrolyte solution. This is explained by the Nernst equation:
\[ E = E^0 - \frac{RT}{nF} \ln Q \]
where:

• \(E\) is the electrode potential,


• \(E^0\) is the standard electrode potential,


• \(R\) is the gas constant,


• \(T\) is the temperature in Kelvin,


• \(n\) is the number of moles of electrons transferred in the half-reaction,


• \(F\) is the Faraday constant,


• \(Q\) is the reaction quotient.

As the concentration of ions changes, \(Q\) changes, leading to a different electrode potential. For example, decreasing the ion concentration lowers the reaction quotient \(Q\), which in turn affects \(E\), making the electrode potential more negative.

Electrolyte Variance in Electrode Potentials

The type of electrolyte in which the electrode operates also impacts the electrode potential. Different electrolytes can have varying ion concentrations and other properties affecting the electrode potential.

• For instance, the presence of impurities in the electrolyte or other chemical interactions within the solution can alter the ion concentration and, by extension, the electrode potential.


• Each electrolyte sets up a distinct environment that can influence the electrode reactions differently, meaning the same electrode can show different potentials when placed in different electrolytes.

Therefore, when comparing electrode potentials, it is crucial to ensure that the electrolyte conditions are standardized to avoid variability.

Temperature Dependence of Electrode Potentials

Temperature directly affects the electrode potentials. According to the Nernst equation, temperature (\(T\)) is a factor that determines the potential:

doubling the temperature increases the thermal energy of the reacting ions, thereby affecting their movement and interaction at the electrode surface.

• Increased temperatures generally increase reaction rates, which can shift the equilibrium position of electrochemical reactions.


• In some cases, higher temperatures make the electrode reactions more favorable, affecting the standard electrode potential \(E^0\).

So, electrode potentials are not independent of temperature; they change as the temperature changes.

Electron Transfer in Electrode Potentials

The number of electrons transferred in an electrochemical reaction greatly influences the electrode potential. This is depicted by the term \(n\) in the Nernst equation.

• The more electrons involved in a half-reaction, the more the potential change per electron transferred, affecting the overall potential observed at the electrode.


• For example, if a redox reaction involves 2 electrons, the potential will be different compared to a reaction involving just 1 electron.


• The relationship between electron transfer and electrode potential is crucial for understanding how batteries, fuel cells, and electroplating processes work.

Therefore, electrode potentials are inherently dependent on the specific number of electrons involved in the electrochemical reaction.