An electrochemical cell is a device that converts the free energy of a spontaneous redox reaction into electrical energy. It consists of two half-cells, each containing an electrode and an electrolyte solution, which are connected by an external circuit and an internal ionic conductor known as a salt bridge.
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The two half-cells in an electrochemical cell are separated by a salt bridge, which allows the flow of ions to maintain electrical neutrality.
The cell potential, or electromotive force (EMF), is the difference between the reduction potentials of the two half-reactions occurring in the cell.
The direction of electron flow in an electrochemical cell is determined by the relative reduction potentials of the two half-reactions.
Electrochemical cells can be classified as voltaic (galvanic) cells, which are spontaneous, or electrolytic cells, which require an external source of energy.
The Nernst equation is used to calculate the cell potential under non-standard conditions, taking into account the concentrations of the reactants and products.
Review Questions
Explain the purpose of the salt bridge in an electrochemical cell.
The salt bridge in an electrochemical cell serves to maintain electrical neutrality by allowing the flow of ions between the two half-cells. As the redox reaction occurs, one half-cell will lose electrons (be oxidized) while the other half-cell will gain electrons (be reduced). The salt bridge allows the movement of ions, such as $\text{K}^{+}$ or $\text{Cl}^{-}$, to balance the charge and prevent the buildup of charge in either half-cell. This ensures that the reaction can proceed continuously and that the cell can generate a stable electrical potential difference.
Describe how the cell potential is determined in an electrochemical cell.
The cell potential, or electromotive force (EMF), of an electrochemical cell is determined by the difference between the reduction potentials of the two half-reactions occurring in the cell. The reduction potential of each half-reaction is a measure of the tendency of the species in that half-reaction to be reduced. By subtracting the reduction potential of the cathode half-reaction from the reduction potential of the anode half-reaction, the overall cell potential is obtained. This cell potential represents the maximum amount of electrical work the cell can perform and is a key factor in determining the spontaneity and feasibility of the redox reaction occurring in the electrochemical cell.
Analyze the factors that influence the direction of electron flow in an electrochemical cell and how this relates to the cell's ability to perform work.
The direction of electron flow in an electrochemical cell is determined by the relative reduction potentials of the two half-reactions. The half-reaction with the more positive reduction potential will be reduced (gain electrons) at the cathode, while the half-reaction with the more negative reduction potential will be oxidized (lose electrons) at the anode. This difference in reduction potentials creates a potential difference, or cell potential, across the cell. The greater the difference in reduction potentials, the higher the cell potential and the more spontaneous the overall redox reaction. A positive cell potential indicates a spontaneous reaction that can generate electrical work, while a negative cell potential indicates a non-spontaneous reaction that requires an external source of energy to proceed. Understanding the relationship between reduction potentials, electron flow, and cell potential is crucial in predicting the behavior and applications of electrochemical cells.
Related terms
Oxidation-Reduction (Redox) Reaction: A chemical reaction in which one reactant loses electrons (is oxidized) while another reactant gains electrons (is reduced).