Cell Potential

Definition

Cell potential, also known as electromotive force (EMF), is the measure of the voltage produced by an electrochemical cell when no current flows. It reflects the tendency of a chemical reaction to occur and is influenced by the nature of the reactants and products, as well as their concentrations. Understanding cell potential is essential for evaluating how effectively an electrochemical cell can convert chemical energy into electrical energy.

5 Must Know Facts For Your Next Test

1. Cell potential can be measured in volts (V) and determines the direction of electron flow in an electrochemical cell.
2. The standard cell potential is calculated using the standard reduction potentials of the half-reactions involved in the overall reaction.
3. A positive cell potential indicates a spontaneous reaction, while a negative cell potential suggests a non-spontaneous reaction.
4. As the concentration of reactants or products changes, the Nernst equation can be used to calculate the effect on cell potential.
5. In concentration cells, the difference in concentration between two solutions creates a driving force for electron transfer, resulting in measurable cell potential.

Review Questions

• How does the Nernst equation relate to cell potential and what role does it play in calculating voltage under non-standard conditions?
  • The Nernst equation provides a relationship between cell potential and the concentrations of reactants and products. It allows us to calculate the actual voltage of an electrochemical cell when conditions deviate from standard conditions. By incorporating concentration changes into the equation, we can predict how variations in reactant or product amounts will affect the overall voltage generated by the cell.
• Discuss how standard reduction potentials are used to determine overall cell potential and explain what a positive or negative value indicates.
  • Standard reduction potentials are essential for calculating overall cell potential by combining the standard reduction potentials of both half-reactions. A positive overall cell potential indicates that the reaction is spontaneous under standard conditions, meaning it can produce electrical energy efficiently. Conversely, a negative value means that the reaction is non-spontaneous, implying that external energy input would be needed to drive the reaction forward.
• Evaluate how variations in ion concentration within a concentration cell can affect its cell potential and explain the underlying principles involved.
  • In a concentration cell, differences in ion concentrations between two half-cells create a gradient that drives electron transfer, leading to a measurable cell potential. As one side has higher concentration, it becomes less favorable for reduction compared to the lower concentration side, which favors reduction. According to the Nernst equation, if concentrations equalize over time, the driving force diminishes and ultimately leads to a decrease in cell potential until it reaches zero when equilibrium is achieved.

Related terms

Standard Reduction Potential: The voltage associated with a reduction half-reaction at standard conditions (1 M concentration, 1 atm pressure, and 25°C), used to predict the spontaneity of redox reactions.

Nernst Equation: A mathematical equation that relates the cell potential to the concentrations of the reactants and products, allowing for calculations under non-standard conditions.

Concentration Cell: A type of electrochemical cell where two half-cells have the same components but different concentrations, resulting in a cell potential based on concentration differences.