Non-spontaneous Redox Reaction

Definition

A non-spontaneous redox reaction is a type of oxidation-reduction reaction that does not occur naturally and requires an external energy input to proceed. These reactions have a positive Gibbs free energy change, indicating that they are not thermodynamically favored to occur on their own.

5 Must Know Facts For Your Next Test

1. Non-spontaneous redox reactions require an external energy input, such as an applied voltage or the coupling with a spontaneous redox reaction, to proceed.
2. The Gibbs free energy change ($\Delta G$) for a non-spontaneous redox reaction is positive, indicating that the reaction is not thermodynamically favorable to occur on its own.
3. The reduction potential ($E^{\circ}$) of a non-spontaneous redox couple is negative, meaning that the reaction has a lower tendency to undergo reduction compared to the standard hydrogen electrode.
4. Non-spontaneous redox reactions can be driven by coupling them with a spontaneous redox reaction that has a more positive reduction potential, in a process known as a galvanic or voltaic cell.
5. The feasibility and direction of a non-spontaneous redox reaction can be determined by comparing the reduction potentials of the reactants and products, as well as the overall Gibbs free energy change of the reaction.

Review Questions

• Explain how the Gibbs free energy change ($\Delta G$) is related to the spontaneity of a redox reaction.
  • The Gibbs free energy change ($\Delta G$) is a key indicator of the spontaneity of a redox reaction. For a non-spontaneous redox reaction, $\Delta G$ is positive, meaning that the reaction is not thermodynamically favorable to occur on its own. The positive $\Delta G$ value indicates that the reaction requires an external energy input, such as an applied voltage or coupling with a spontaneous redox reaction, in order to proceed. In contrast, a spontaneous redox reaction has a negative $\Delta G$, making it thermodynamically favorable and able to occur naturally without any external energy input.
• Describe how the reduction potential ($E^{\circ}$) of a non-spontaneous redox couple is related to the spontaneity of the reaction.
  • The reduction potential ($E^{\circ}$) of a non-spontaneous redox couple is a measure of the tendency of the chemical species to undergo reduction (gain electrons) in an electrochemical reaction. For a non-spontaneous redox reaction, the reduction potential of the redox couple is negative, indicating that the reaction has a lower tendency to undergo reduction compared to the standard hydrogen electrode. This negative reduction potential is directly related to the positive Gibbs free energy change ($\Delta G$) of the non-spontaneous redox reaction, as the two properties are inversely related. The lower reduction potential of the non-spontaneous redox couple means that the reaction is not thermodynamically favorable to occur naturally and requires an external energy input to proceed.
• Explain how a non-spontaneous redox reaction can be driven by coupling it with a spontaneous redox reaction in a galvanic or voltaic cell.
  • Non-spontaneous redox reactions can be driven by coupling them with a spontaneous redox reaction that has a more positive reduction potential. This process occurs in a galvanic or voltaic cell, where the spontaneous redox reaction provides the necessary energy to drive the non-spontaneous redox reaction. The spontaneous redox reaction, which has a negative Gibbs free energy change ($\Delta G < 0$), provides the driving force for the non-spontaneous redox reaction, which has a positive $\Delta G$. The overall cell reaction is a combination of the two redox reactions, with the spontaneous reaction providing the energy needed to make the non-spontaneous reaction feasible. This coupling of redox reactions allows for the generation of an electrical current, which can be used to perform work or store energy.

Related terms

Spontaneous Redox Reaction: A spontaneous redox reaction is an oxidation-reduction reaction that occurs naturally without the need for external energy input. These reactions have a negative Gibbs free energy change, making them thermodynamically favorable.

Gibbs Free Energy: Gibbs free energy is a thermodynamic property that combines the concepts of enthalpy and entropy to determine the spontaneity and feasibility of a chemical reaction. It is calculated as the difference between the enthalpy and the product of temperature and entropy.

Electrochemical Potential: Electrochemical potential, also known as reduction potential or redox potential, is a measure of the tendency of a chemical species to undergo reduction (gain electrons) in an electrochemical reaction. It is used to determine the spontaneity and direction of redox reactions.