To determine when a reaction is spontaneous based on cell potential, we need to consider the concept of electrochemical cells and their potential, often referred to as the electromotive force (EMF) of a cell.
In electrochemistry, the cell potential (or EMF) indicates the tendency of a cell to drive an electric current. The standard cell potential is a measure of the driving force behind a chemical reaction occurring in an electrochemical cell.
- The spontaneity of a chemical reaction is usually determined by the Gibbs free energy change (\(\Delta G\)), where a negative \(\Delta G\) indicates a spontaneous reaction.
- The Gibbs free energy change is related to the cell potential (\(E_{\text{cell}}\)) by the equation:
\(\Delta G = -nFE_{\text{cell}}\)
- Where:
- \(\Delta G\) is the change in Gibbs free energy,
- \(n\) is the number of moles of electrons transferred in the reaction,
- \(F\) is Faraday's constant (approximately \(96485 \, C/mol\)),
- \(E_{\text{cell}}\) is the cell potential in volts.
- If \(E_{\text{cell}}\) is positive, then \(\Delta G\) is negative, indicating that the reaction is spontaneous.
- Therefore, a positive cell potential corresponds to a spontaneous reaction. Conversely, if the cell potential is negative or zero, the reaction is non-spontaneous or at equilibrium, respectively.
Thus, the correct answer is that the reaction is spontaneous if the cell potential is positive.