In electrochemistry, the voltaic cell and the electrolytic cell are both electrochemical cells.Here, we learn how each of these cells works and then do a voltaic vs. electrolytic comparison by listing out their similarities and differences.
The electrochemical cells at the heart of electrochemistry are the voltaic and electrolytic cells.In this article, we'll look at the workings of voltaic and electrolytic cells and highlight their similarities and differences.
Did You Know?
Galvanic cells are also known as voltaic cells.Names derived from pioneers of this technology, Alessandro Volta and Luigi Galvini.
First, one must study the local pond before one attempts to study the ocean.A similar rule applies to electrochemistry.
.Electrochemical cells are used for many specialized processes today, including the powering of phones, laptops, cars, inverters, etc. They are also used for electrolysis and electroplating.
There are two basic types of cells - the voltaic cell and the electrolytic cell.The former explains how modern-day batteries work while the latter describes how cells are used in specific applications.These two types of cells are discussed in greater detail in the following sections.
The Voltaic Cell
As an example of an electrochemical cell, a voltaic cell can be considered.It is classified as such because, within it, a chemical reaction occurs that generates proportional electrical energy.Battery technology today is based on the voltaic cell.
The following is the working principle of a basic voltaic cell.
Molecular reactions occur when two dissimilar metal plates are immersed together in an electrolytic solution, with the one with higher reactivity reacting with the electrolyte.As a result, the positively charged ions dissolve into it, leaving behind free electrons.It becomes negatively charged as a consequence.
The other metal plate which has a lower reactivity, will tend to attract these positive ions present in the electrolyte which will get deposited on its surface, making it positively charged.
Once a conductor is connected externally to these two metal plates, the current begins to flow.In simple terms, the current is directly proportional to the amount of positive and negative charge on the respective metal plates.
Simple Voltaic Cell: Construction and Working
Diagram showing the main elements used to construct a simple voltaic cell.An electrolyte is formed by adding a solution of sulfuric acid (H2SO4) to a container.Two electrodes are immersed in the solution.The electrodes are made of zinc (Zn) and copper (Cu).Between these two electrodes, as shown in the diagram, is an external conductor.
Voltaic Cell Working
Zinc has a higher reactivity with sulfuric acid than copper.It is dissolved slowly in an electrolyte solution in the form of positive zinc ions and leaves behind free electrons on the zinc electrode.It occurs spontaneously until an equilibrium between the number of zinc ions produced and the number of zinc ions returning to the electrode is reached.The voltage of the zinc electrode is (-0.62V) at this point.It follows this reaction equation.
At Zinc Electrode: Zn –> Zn++ + 2 e—
(H2SO4) contains molecular bonds between hydrogen and sulfur which zinc ions dissolve and react with the negative SO4 ions of the electrolyte.The resulting protonate is ZnSO4.The chemical reaction at the zinc electrode is illustrated below.
In the Sulfuric Acid Solution: H2SO4 –> 2H+ + SO4—
Zn++ + SO4— –> ZnSO4
In the electrolytic solution, hydrogen ions get dispersed that have been freed from sulfuric acid.The copper electrode reacts with them, extracting electrons to produce hydrogen gas which bubbles out of the solution.Pictured below is the reaction.
At Copper electrode: 2H+ + 2e– –> H2gas
As time passes, the copper electrode develops a positive potential, which repels the positive hydrogen ions, and electrons start losing their electrons.At this point, an electrical charge of 0.46V is applied to the copper plate.
As a result, the total potential difference between the two electrodes is +0.46 – (0.62) > = 1.08V.Voltaic cells have electromotive forces (EF).By connecting a conductor externally between two electrodes, a current will flow through it when the switch is closed, and the bulb will turn on.
Electrolytic cells are another type of electrochemical cell.Yet it works in a complete opposite way from a voltaic cell.By using a potential difference externally, an electrolytic cell instead of producing electricity through chemical reaction drives a useful chemical reaction.
The following is its working principle.
An electrolytic cell is used for electrolysis.A Greek suffix -lysis means splitting.An electrolysis is therefore the process by which a compound is broken up into its constituent elements by means of electrical energy.
An electrolyte is generally used in electrolytic cells to separate the compounds.Two inert electrodes are immersed in an electrolyte solution, and an external voltage source is used to create a potential difference between them.As a result, one electrode becomes positively charged, while the other becomes negatively charged.
.In this way, electrical energy can be used to split up a compound by electrolysis.The whole idea behind an electrolytic cell is the same.
Simple Electrolytic Cell: Construction and Working
For our example, we will split salt (NaCl).The salt crystals are first melted by heating it.A container of electrolysis is then filled with this melted liquid.
.The positively charged electrode attracts the negative chlorine ions (Cl–), whereas the negatively charged electrode attracts the positive sodium ions (Na+).
By contacting the negatively charged electrode with (Na+) ions, these ions acquire electrons from the electrode and become sodium (Na) metal, which is deposited on the electrode.Equation 15 describes this process.
At the Cathode: Na++ + e– –> Na
Similarly, when (Cl–) ions reach the positively charged electrode, they lose electrons and get oxidized to chlorine gas, which bubbles out of the solution. This is shown in the equation below.
At the Anode: 2Cl– –> + Cl2 + e–
Thus effectively, the compound NaCl gets split into its constituent elements of Na and Cl in an electrolytic cell.
Electrolysis of Salt: 2 NaCl –> 2Na + Cl2 (gas)
Note: The potential required to oxidize (Cl–) ions to Cl2 is 1.36V, while that required to reduce (Na+) ions to sodium metal is (- 2.71V). Thus, the battery required to carry out this reaction needs to be at least <1.36 – (- 2.71)> = 4.07V.
Similarities Between Voltaic Cell and Electrolytic Cell
In both voltaic and electrolytic cells, oxidation occurs at the anode, while reduction occurs at the cathode.Both of these cells exhibit redox reactions.
2) Direction of Electron FlowIn both these cells, electrons flow from the anode to the cathode through the externally connected conductor.
Differences Between Voltaic Cell and Electrolytic Cell
Electric Energy and Chemical Reaction
To generate electrical energy in a voltaic cell, a chemical reaction is used.An electrolytic cell uses an external potential difference to drive a chemical reaction.
In voltaic cells, the two electrodes need to be made out of two different metals, with one being more reactive to the electrolytic compound as compared to the other. Typically, in electrolytic cells, both the electrodes used are made of the same inert metal (graphite or platinum).
Conversion of Energy
In voltaic cells, chemical energy is converted to proportional electric energy, while in the electrolytic cells, electric energy is converted to chemical energy.
Anode and Cathode Polarities
Voltaic cells have a negatively charged anode and a positively charged cathode. Electrolytic cells have a positively charged anode and a negatively charged cathode.
Spontaneity of Reaction
In voltaic cells, the chemical reaction leading to the generation of electrical energy occurs spontaneously. Conversely, in an electrolytic cell, an external emf source has to be used to drive the chemical reaction.
Voltaic cells and electrolytic cells are two different types of electrochemical cells that serve different purposes.Several modern-day batteries and other electrochemical applications have been designed and built using these types of batteries.