Electrochemical Chemistry

Electrochemistry is that branch of chemistry which deals with the conversion of electrical energy into chemical energy and vice versa. A chemical reaction occurs when an electric current is conducted through an aqueous solution of particular chemicals or through molten salts. Further, chemical reactions are responsible for electrical energy in dry cells, button cells, and lead acid batteries. In this lesson you will learn about some characteristics of these processes.

Electrochemical Cells:

A spontaneous chemical process is one that can occur on its own, and in such a reaction, the system’s Gibbs energy falls. This energy is then converted into electrical energy. The reverse reaction is suitable where we can create non-spontaneous cycles to take place by producing external energy as electrical energy. 

Electrochemical Cells are utilised to do these interconversions. An electrochemical cell is a device that generates electrical energy through chemical reactions. The electrical energy delivered to electrochemical cells is used to smoothen chemical reactions. The devices in an electrochemical cell have the ability to convert chemical energy to electrical energy or vice versa.

Types:

Electrochemical Cells are further divided into two categories:

1. Galvanic Cells :- Transforms chemical energy into electrical energy.
2. Electrolytic Cells :- Transforms electrical energy into chemical energy.

Galvanic Cells:

Cell energy is drawn out from a spontaneous chemical process or reaction and this is then converted to electric current. For example, Daniell Cell is a Galvanic Cell in which Zinc and Copper are utilised for the redox reaction to take place.

Zn(s) + Cu²⁺ → (aq) Zn²⁺ (aq) + Cu(s) 

Oxidation Half : Zn(s) → Zn²⁺ (aq) + 2e⁻ 

Reduction Half : Cu²⁺(aq) + 2e⁻ → Cu(s)

Zn is the reducing agent and Cu²⁺ is the oxidising agent.The half cells are also identified as Electrodes. The oxidation half is called  Anode and the reduction half is called Cathode. Electrons move from anode to cathode in the external circuit. Anode is said to have negative polarity and cathode is said to have positive polarity. In Daniell Cell, Zn goes about as the anode and Cu goes about as the cathode.

Electrolytic Cell:

In this process, electrodes are dipped in an electrolytic solution containing cations and anions. On providing electric current the ions progress towards electrodes of opposite polarity and simultaneous reduction and oxidation takes place.

Electrode Potential:

Electrode Potential is the tendency of an element when put in touch with its own ions to either lose or acquire electrons and thus become positively or negatively charged. The electrode potential is named as oxidation or reduction potential relying upon whether oxidation or reduction has happened. 

M(s) ⇌ Mⁿ⁺(aq) + ne⁻

Mⁿ⁺(aq) + ne⁻ ⇌ M(s)

Oxidation Potential:

Oxidation potential is the propensity to lose electrons. Oxidation potential of a half-cell is inversely proportional to the concentration of ions within the solution.

Reduction Potential:

Reduction potential is the propensity to gain electrons. According to IUPAC convention, the reduction potential alone can be called the electrode potential unless it is specifically mentioned. 

Standard Electrode Potential (Eº):

Standard Electrode Potential is the electrode potential of an electrode decided comparative with standard hydrogen electrode under standard conditions. 

The standard conditions taken are :

(i) 1M concentration of each ion in the solution. 

(ii) A temperature of 298 K. 

(iii) 1 bar pressure for each gas.

Cell Potential or EMF of a Cell:

EMF or Electromotive Force of a cell is the contrast between the electrode potentials of two half-cells and causes a stream of current from electrode at higher potential to electrode at lower potential. It is additionally the proportion of free energy change.

Ecell = Ecathode + Eanode

For this equation we use oxidation potential of anode and reduction potential of cathode.

Since anode is put on left and cathode on right, it follows therefore,

 = Er + El 

Conclusion:

In this chapter, we have covered all the fundamental topics of electrochemistry. We reviewed the behaviour of a wide range of types of electrochemical cells which are used in various fields. Galvanic cells rely on spontaneous oxidation–reduction reactions to produce current and provide energy. The concentration cell is a type of galvanic cell in which the current is determined by an ion concentration gradient rather than a difference in reduction potential between two chemically distinct electrodes. Electrolytic cells rely on external voltage sources to power electrolysis, a nonspontaneous oxidation–reduction reaction. Finally, we looked at the thermodynamics of various cell types. Electrolytic cells have negative electromotive forces (emf) and positive free energy changes, whereas galvanic and concentration cells have positive emf and negative free energy changes.