Intro to Electrochemical Cells: Videos & Practice Problems

Electrochemical Cells Example

In electrochemical cells, the standard cell potential is a crucial factor in determining whether a cell consumes or generates electricity. When evaluating which cell uses up the largest quantity of electricity at 25 degrees Celsius, it is essential to focus on the sign and magnitude of the standard cell potential. A negative standard cell potential indicates that the cell is consuming electricity, while a positive value suggests that it is generating electricity.

In this scenario, options with negative standard cell potentials are considered, specifically those with values of -0.75 volts and -1.42 volts. Among these, the cell with the most negative standard cell potential, which is -1.42 volts, indicates the highest consumption of electricity. Therefore, the electrochemical cell that uses up the largest quantity of electricity is the one with the standard cell potential of -1.42 volts.

In summary, when assessing electrochemical cells, remember that a more negative standard cell potential correlates with greater electricity consumption. Thus, the correct answer is the cell with the standard cell potential of -1.42 volts.

Here's what students ask on this topic:

What is an electrochemical cell and how does it work?

An electrochemical cell is a device composed of two half-cells, each containing an electrode immersed in an electrolyte solution. In one half-cell, oxidation occurs, where a metal electrode loses electrons and forms positive ions. In the other half-cell, reduction takes place, where positive ions gain electrons and become neutral atoms. These two half-cells are connected by a conductive wire, allowing electrons to flow from the oxidation half-cell to the reduction half-cell. This flow of electrons generates electricity. The overall process is a redox reaction, involving the transfer of electrons between the two half-cells. The movement of electrons through the wire produces or consumes electrical energy depending on the type of cell.

What is cell potential and how is it measured in electrochemical cells?

Cell potential, denoted as $E_{\mathrm{cell}}$, is the difference in potential energy between two half-cells in an electrochemical cell. It represents the driving force for electron flow from the oxidation half-cell to the reduction half-cell. Cell potential is measured in volts (V). Under standard conditions (25°C, 1 M concentration, 1 atm pressure, and pH 7), the standard cell potential is written as $E_{\mathrm{cell}}°$. If conditions deviate from these, the cell potential is non-standard and written without the degree symbol. A positive cell potential indicates a spontaneous reaction producing electricity, while a negative value means the cell consumes electricity.

What are the differences between galvanic and electrolytic cells?

Galvanic and electrolytic cells are two types of electrochemical cells distinguished by their cell potentials and functions. A galvanic cell has a positive cell potential ($E_{\mathrm{cell}}>\; 0$) and spontaneously produces electricity by converting chemical energy into electrical energy. It consists of two half-cells where oxidation and reduction occur naturally, driving electron flow through an external circuit. In contrast, an electrolytic cell has a negative cell potential () and requires an external power source to drive a non-spontaneous redox reaction. It consumes electrical energy to cause chemical changes, such as electroplating or decomposition of compounds.

How do oxidation and reduction occur in the half-cells of an electrochemical cell?

In an electrochemical cell, oxidation and reduction occur in separate half-cells. Oxidation happens at the anode, where a solid metal electrode loses electrons and forms positive ions. For example, a metal $M$ can oxidize as $M(s)\to M^{+}+e-$. This increases the oxidation state of the metal. Reduction occurs at the cathode, where positive ions in solution gain electrons to form neutral atoms, such as $X^{+}+e-\to X(s)$. This decreases the oxidation state. The electrons lost in oxidation travel through the external wire to the reduction half-cell, completing the redox reaction and generating electrical current.

What are standard conditions for measuring cell potential in electrochemical cells?

Standard conditions for measuring cell potential in electrochemical cells are defined as a temperature of 25°C (298 K), 1 molar (1 M) concentration for all aqueous species, 1 atmosphere (1 atm) pressure for any gases involved, and a pH of 7 for solutions. Under these conditions, the cell potential is called the standard cell potential and is denoted as $E_{\mathrm{cell}}°$. These conditions provide a consistent basis for comparing the potentials of different electrochemical cells. Deviations from these conditions result in non-standard cell potentials, which can be calculated using the Nernst equation.