Electrochemical cells


       Electrochemical cells
Galvanic and Electrolytic Cells

Oxidation-reduction reaction or redox reactions occur in electrochemical cells. There are two different kinds of electrochemical cells. Spontaneous reactions take place in galvanic (voltaic) cells; non-spontaneous reactions take place in electrolytic cells. The two types of cells have electrodes where the oxidation and reduction reactions take place. Oxidation takes place at the electrode referred the anode and reduction takes place at the electrode known as the cathode.

Electrodes and Charge

The anode of an electrolytic cell is positive electrode while cathode is negative electrode, since the anode pull anions towards you from the solution. Nevertheless, the anode of a galvanic cell is negatively charged, since the spontaneous oxidation at the anode is the basis of the cell’s electrons or negative charge. The cathode of a galvanic cell is its positive pole. In the 2cells- galvanic and electrolytic cells, oxidation occurs at the anode and electrons movement is from the anode to the cathode.

Galvanic or Voltaic Cells

The redox or reduction-oxidation reaction in a galvanic cell is a spontaneous reaction. Therefore, galvanic cells are normally used as batteries. Galvanic cell reactions provide energy which is utilized to carry out work. The energy is harvested by positioning the oxidation and reduction reactions in different containers, connected by an apparatus that permits electrons to flow. A widespread galvanic cell is the Daniell cell, illustrated below.

Electrolytic Cells

The redox reaction or reduction-oxidation reaction in an electrolytic cell is non spontaneous. Electrical energy is needed to stimulate the electrolysis reaction. A sample of an electrolytic cell is illustrated below with a molten NaCl that is electrolyzed to form liquid sodium and chlorine gas. The sodium ions wander toward the cathode, the electrode at which they are reduced to sodium metal. Likewise, chloride ions move to the anode and are oxidized to form chlorine gas. This sort of cell is used to generate sodium and chlorine. The chlorine gas can be gathered near the cell. The sodium metal is less heavy than the molten salt and is therefore taken away as it floats to the apex of the reaction container.

Electrolysis is the passage of a direct electric current through an ionic compound that is either in molten form or dissolved in an appropriate solvent, leading to chemical reactions at the electrodes and disconnection of materials.

The major components necessary to attain electrolysis are :

• An electrolyte : An electrolyte is a substance that contains free ions that are the carriers of electric current in the electrolyte. If the ions are not in motion like in a solid salt electrolysis cannot take place.

• A direct current (DC) supply: makes available the energy required to generate or discharge the ions in the electrolyte. Electric current is carried by electrons in the external circuit.

• Two electrodes: Electrodes are electrical conductor that produces the physical boundary between the electrical circuit making available the energy and the electrolyte.

Electrodes of metal, graphite and semiconductor substance are extensively used. Selection of appropriate electrode depends on chemical reactivity between the electrode and electrolyte and the asking price of production.

Process of electrolysis

The main process of electrolysis is the substitution of atoms and ions through the removal or addition of electrons from the external circuit. The preferred products of electrolysis are frequently in a dissimilar physical state from the electrolyte and can be separated by a number of physical processes. For instance, in the electrolysis of brine that yields hydrogen and chlorine, the resulting product are gaseous. These gaseous products bubble from the electrolyte and are collected.

2 NaCl + 2 H2O → 2 NaOH + H2 + Cl2

A liquid containing mobile ions (electrolyte) is manufactured by:

• Solvation or reaction of an ionic compound with a solvent like water to give rise to mobile ions.

• An ionic compound is dissolved or merged by heating

An electrical potential is applied crosswise a pair of electrodes engrossed in the electrolyte.

Every one of the electrodes attracts ions that have differing charge. Positively charged ions (cations) move towards the electron-supplying (negative) cathode, while negatively charged ions (anions) drift towards the positive anode.

At the electrodes, electrons are taken or given out by the atoms and ions. Those atoms that gain or lose electrons to turn into charged ions move into the electrolyte. Those ions that gain or lose electrons to turn into uncharged atoms split from the electrolyte. The production of uncharged atoms from ions is referred to as discharging.

The energy that is needed to make the ions to travel to the electrodes, and the energy to result to the change in ionic state, is made available by the external supply of electrical potential.

Oxidation and reduction at the electrodes

Oxidation of ions or neutral molecules takes place at the anode, and the reduction of ions or neutral molecules takes place at the cathode. For instance, it is probable to oxidize ferrous ions to ferric ions at the anode:

Fe2+ aq → Fe3+ aq + e-
It is as well likely to reduce ferricyanide ions to ferrocyanide ions at the cathode:

Fe(CN)3-6 + e– → Fe(CN)4-6

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