Electrochemistry Chemistry Notes
→ The branch of chemistry, by which we study relation between chemical energy and electric energy of a process and their interchange in each other, is called electrochemistry, The reactions of these types of processes is redox reactions. Electrochemistry is very useful for industries.
→ The formation of compounds like NaOH, Cl2, F2 etc., from most active metals like Na, Mg. Al etc., is performed by electrochemical methods. Batteries, fuel cells etc., are used for energy. Environment is not much polluted by using them.
→ Electrochemical reactions are very useful for invention of new techniques. If we think then we will find that electrochemistry is the basis for movement of noise impulses from cell to brain and brain to cell. So, electrochemistry is a detailed and interdisciplinary subject.
Chapter in Brief and Glossary :
- Electrochemical cell—The apparatus or cell or electrochemical device by which we convert chemical energy into electric energy, is called Galvanic or voltaic or electrochemical cell.
- Half-cell-The cell in which oxidation or reduction reaction takes place, is called half-cell. If oxidation reaction takes place then it is called oxidation half-cell and if reduction reaction takes place then it is called reduction half-reaction.
- Inert Electrolyte-The electrolyte which does not represent any chemical reaction during process is called inert electrolyte. Example : KCI, KNO3, NH4NO3 etc.
- Salt Bridge-It is a U-shape tube made up of glass. It contains concentrated solution of inert electrolyte like KCl, KNO3 etc.
- Electrode Potential – The potential difference produced between solution of metal and metal ions is called electrode potential
- Oxidation Potential-If oxidation takes place at metal rod then it is called oxidation potential.
- Reduction PotentialIf reduction takes place at metal rod then it is called reduction potential,
- Standard Electrode Potential-The electrode potential in a metal ion solution of 1 mol L-1 concentration at 298 K in a half-cell is called standard electrode potential
- Standard Reduction Potential-The tendency of an electrode to reduce or accept electron in 1 mol L-1 concentration at 298 K is called its standard reduction potential.
- Standard Oxidation Potential-The tendency of an electrode to oxidise or donate electron in 1 mol L-1 concentration at 298 K is called its standard oxidation potential.
- Electromotive Force or Cell Potential The potential difference between both electrodes of an electrochemical cell is called electromotive force of cell. It is measured in volt. At this time, no current flows.
- Electrochemical Series The series which is obtained from arranging various metals in increasing or decreasing order of standard electrode potential, is called electrochemical series.
- Electrolytic Conduction-The property of flowing electricity in an electrolytic solution or its molten state is called electrolytic conduction.
- Ohm’s Law-According to this law, electric current passing in electrolytic conductor is inversely proportional to the resistance of conductor
- Conductivity-It is reciprocal to resistance.
- Specific Resistance or Resistivity-Specific resistance of an electrolytic conductor is that resistance in ohm when length of conductor is 1 cm and area of cross-section is 1 cm2 i.e. the resistance of 1 cm3 electrolytic solution is called it specific resistance.
- Specific Conductivity Specific conductivity is the reciprocal of specific resistance of an electrolytic conductor. In other words, the specific conductivity of an electrolytic solution is that conductance when solution is placed between two electrodes apart from 1 cm having 1 cm area of cross-section
- Cell Constant-The ratio of distance between two parallel electrodes and area of cross-section of electrodes of a cell (WA) is called cell constant.
- Molar Conductivity-The conductivity of the solution present between two electrodes placed 1 cm2 apart having 1 cm area of cross section in which one gram molecular mass of electrolyte is dissolved, is called its molar conductivity.
- Equivalent Conductivity-The conductivity of that volume of solution present between two electrodes placed 1 cm apart having certain area in which one gram equivalent of electrolyte is dissolved, is called its equivalent conductivity.
- Conductors-Those substances in which flow of electric current is possible, are called conductors.
- Metallic Conductors-Those metallic substances in which electric current is passed without any chemical change, are called metallic conductors. Example : Cu, Ag, Au etc.
- Electrolyte-The substance in which flow of electric current is possible in its molten state or aqueous solution, is called electrolyte. Example : NaCl, KCl, KNO3 etc.
- Insulators-Those substances which do not conduct electricity are called insulators. Example: Glass, Plastic etc.
- Semiconductors-Those substances whose conductivity lies in between conductors and insulators, are calles semiconductors. Example : Silicon (Si), Germanium (Ge) etc.
- Superconductors-Those substances which have zero resistivity or infinite conductivity, are called superconductors.
- Strong Electrolytes – Those electrolytes which dissociate completely in ions in solution, are called strong electrolytes. Example : NaCl, KCI, HCI, KNO3 etc.
- Weak Electrolytes-Those electrolytes which do not dissociate completely in solution, are called weak electrolytes. Example:CH3COOH, NH4OH, ZnCl2 etc.
- Kohlrausch’s Law-According to this law, the limiting molar conductivity of an electrolyte can be represented by the sum of contribution molar conductiviting of its cations and anions.
- Electrolytic Cell-The device which can be used to convert electric energy into chemical energy, is called electrolytic cell.
- Faraday’s First Law of Electrolysis-According to this law, the amount of substance liberated at electrode is directly proportional to quantity of electric current passed in electrolytic solution.
- Faraday’s Second Law of Electrolysis According to this law, when same quantity of electricity is passed in various electrolytic solutions arranged in series, then weights of substances produced at electrodes are directly proportional to their chemical equivalent weights.
- Battery-When more then one cells are arranged in series then battery is formed. Infact, battery is an arrangement of Galvanic cells arranged in series. Battery converts chemical energy of redox reaction into electric energy.
- Primary Batteries-Reaction takes place only once in primary batteries and battery becomes inactive after some time and can not be used again.
- Secondary Batteries-There are reversible Galvanic cells. In these batteries, substances having high energy produce electric current become and become inactive.
- Their substances make active again by external sources and substances can be reused again in cell. These cells can be recharged again. Strong battery can be discharged and charged many times.
- Fuel Cell-Fuel cell is like that of primary cell. In this cell, combustion of fuel takes place and chemical energy produced in it, is converted into electrical energy
- Corrosion-The process in which oxides, carbonates, sulphates etc., are formed at the surface of metal by the attack of atmospheric gases or water vapour and metal corrodes slowly then this process is called corrosion.
- Examples : Tarnishing of silver, formation of green layer on copper etc.