Intro to Electrochemical Cells - Online Tutor, Practice Problems & Exam Prep

An electrochemical cell consists of two half-cells, each containing an electrode immersed in an electrolyte, where redox reactions occur. Oxidation happens at one electrode, involving the loss of electrons, while reduction occurs at the other, where electrons are gained. The movement of electrons between the half-cells through a conductive wire generates or consumes electricity. The cell potential, measured in volts (V), indicates the energy difference as electrons move between half-cells. Under standard conditions (25°C, 1 M, 1 atm, pH=7), the standard cell potential (E^°_cell) is used, while non-standard conditions yield a non-standard cell potential. There are two types of electrochemical cells: galvanic cells, which have a positive cell potential and produce electricity, and electrolytic cells, with a negative cell potential, consuming electricity.

Electrochemical Cells

Now an electrochemical cell is just an instrument composed of two half cells connected by a conductive wire. Now here if we take a look at this image, two half cells, this is 12 cell which is in this jar and this is our second-half cell which is our second jar. They're connected by a conductive wire. Now within each one of these jars or half cells, we have a metal rod which is our electrode. They're connected together by this conductive wire here where electrons travel.

Now here 12 cell is a container with a single electrode, so that's that metal rod immersed in an electrolyte solution representing 12 reaction. Now here if we go back down here we can say in this first half cell jar we have involved M solid electrode and dissolved within the solution our M plus ions. Here if we take a look at the half reaction we have M solid giving us M positive plus on an electron. When you have an electron as a product that represents an oxidation, and that's because the oxidation number of my rod is increasing, you go from neutral, which is 0 oxidation state, to here A + 1 oxidation state. Your oxidation number increase, so that's oxidation.

On the other side we have an X electrode rod and to solve X plus ions here we're going from plus one to neutral, so zero. My oxidation number decreased, so I'm being reduced. So this half cell deals with reduction. So we have one doing oxidation, one doing reduction. So we have in essence is a redox reaction. So we're going to say through a redox reaction, the transferring of electrons between half cells produces or consumes electricity. Electricity is just the movement of electrons across conductive wires like we have here in this electrochemical cell.

So oxidations were losing electrons, so electrons would literally leave this part and travel to the other half cell reduction occurs. So these are just some fundamental key steps when a within a typical electrochemical cell we're going to go into greater detail, but for right now just remember that an electrochemical cell has two jars to have cells. One is where oxidation occurs and the other is where reduction occurs. The movement of electrons can either produce or consume electricity in this process.

Cell Potential and Spontaneity

Here we're going to say that an electrochemical cell is what we call a cell potential. Now this cell potential will be under standard conditions or non-standard conditions. Cell potential is Ecell. If it's under standard conditions we use not a little circle here or zero. If it's non-standard conditions, it doesn't have that little knot or circle.

Now cell potential is just the difference in potential energies as electrons travel between the half cells. Remember 1/2 cell deals with oxidation where we're losing electrons. The other one deals with reduction when we're gaining electrons. The traveling of the electrons is what creates potentially electricity. Now here this will be measured in volts. So volts here will be using the variable V.

Now recall standard conditions are 25°C, one molar, one atmosphere and pH equal to seven. Under these conditions we'd use this cell potential. If we aren't following these standard conditions then we're talking about non-standard cell potential. Now there are two types of electrochemical cells, one that produces electricity so makes it and one that consumes electricity so uses it up.

These two types of electrochemical cells have names given to them, so one is called a galvanic cell. This one has a cell potential that is positive, whether that be standard or non-standard, meaning electricity is produced. So if we have an electrochemical cell that is positive in terms of its cell potential, it represents a galvanic cell. Galvanic cells produce electricity.

An electrolytic cell, by contrast, would have a cell potential that is negative. Because of this, it doesn't produce electricity. It consumes or uses it up. So just remember we have standard cell potential and non-standard cell potential and then we have two types of electrochemical cells based on the idea of either making or producing electricity. So those will be our galvanic cells or consuming or using up electricity. Those would be our electrolytic cells.

Intro to Electrochemical Cells Example

Which of the following electrochemical cells would use up the largest quantity of electricity at 25°C? All right, so here they're saying would use up. This means that it's consuming electricity. Here we have electrochemical cells A to D, each with a standard cell potential, some being negative, some being positive.

Remember, if you're using up electricity, you're consuming electricity, which means that your standard cell potential would be negative. That means that options B&C are out. Here we have -0.75 V versus -1.42 V.

Here D is the answer because not only is it negative in terms of its standard cell potential, it is the most negative. This would mean that it consumes or uses up the largest amount of electricity. So again, our final answer here would be option D.

Here’s what students ask on this topic:

Which statement describes the two types of reactions that occur in operating electrochemical cells?

In operating electrochemical cells, two types of reactions occur: oxidation and reduction reactions, which together are referred to as redox reactions. Oxidation is the process by which a substance loses electrons, while reduction is the process by which a substance gains electrons. These reactions occur simultaneously and are spatially separated in different parts of the cell. In a typical electrochemical cell, the oxidation reaction takes place at the anode, and the reduction reaction occurs at the cathode. Electrons flow through an external circuit from the anode to the cathode, while ions move through an electrolyte to maintain charge balance. The movement of electrons through the external circuit generates an electric current, which can be harnessed to do work.

What are electrochemical cells?

Electrochemical cells are devices that convert chemical energy into electrical energy or vice versa through redox reactions, which involve the transfer of electrons. There are two main types of electrochemical cells: galvanic (or voltaic) cells and electrolytic cells.

Galvanic cells harness the energy from spontaneous chemical reactions to generate electricity. They consist of two different metals connected by a salt bridge or a porous membrane and immersed in electrolyte solutions. The metals act as electrodes, with the anode undergoing oxidation (loss of electrons) and the cathode undergoing reduction (gain of electrons). The flow of electrons from the anode to the cathode through an external circuit generates an electric current.

Electrolytic cells, on the other hand, use electrical energy to drive non-spontaneous chemical reactions. They are often used for processes such as electroplating or the decomposition of compounds. In these cells, an external voltage is applied to force electrons to move in the opposite direction to a galvanic cell, causing chemical changes at the electrodes.

Both types of cells are fundamental in various applications, from batteries and fuel cells to metal refining and electroplating industries.

How do electrochemical cells work?

Electrochemical cells convert chemical energy into electrical energy through redox reactions. These cells consist of two electrodes (an anode and a cathode) and an electrolyte that allows ions to move between the electrodes.

In an electrochemical cell, the anode is the electrode where oxidation (loss of electrons) occurs, and the cathode is where reduction (gain of electrons) takes place. When the cell operates, electrons flow from the anode to the cathode through an external circuit, providing electrical energy that can do work, like powering a light bulb.

The electrolyte, often a liquid or paste, contains ions that move to balance the charge: positive ions (cations) move towards the cathode, and negative ions (anions) move towards the anode. This movement completes the circuit internally, allowing the cell to continue operating.

The specific materials used for the electrodes and the electrolyte, as well as their arrangement, determine the voltage and capacity of the electrochemical cell. Common examples include the lead-acid batteries in cars and lithium-ion batteries in smartphones and laptops.