Electrochemistry State NCERT Solutions for Class 12 Chemistry Chapter 3
Prasanna
Chemical Kinetics Chemistry Notes
Chemical Kinetics Chemistry Notes
Introduction :
→ We know that in a chemical reaction, a substance having specific properties is converted into other substances whose properties are different. Chemists are always qurious to know about following details :
- A chemical reaction is possible or not in the given conditions. It is determined by thermodynamics. If the value of Gibbs free energy is negative (-4G) then reaction will be possible or not.
- How much part of reactants can be converted into products. It can not be answered by chemical equilibrium.
- How much time will be required to complete the reaction or reach to equilibrium?
→ Above facts can be determined with the help of given conditions like-pressure, temperature, concentration, catalyst etc. These conditions are also helpful for determining reaction mechanism.
→ Chemical reactions take place with various rates. So, the branch of chemistry which deals with the rates of chemical reactions, mechanism and factors affecting them is called chemical kinetics. The term ‘kinetics’ is derived from Greek word ‘kinesis’, which means rate. So, chemical kinetics determines rate of reaction.
Chapter in Brief and Glossary :
→ Ionic or Instantaneous Reactions : The reactions which take place between ions and possess high rate of reaction, are called ionic reactions.
Example : NaCl(aq) + AgNO3(aq) — AgCl(s) + NaNO3(aq)
→ Very Slow Reactions : These reactions occur between molecules. Their rate is very slow. So, there is no measurable change in these reactions.
Example : Formation of water by combination of hydrogen and oxygen in the absence of catalyst.
→ Molecular or Slow Reactions : Those reactions which take place between molecules, are called molecular reactions. Their rates can be determined.
Example:
→ Rate of Reaction: The change in concentration of a reactant or product in unit time is called rate of reaction. Its unit is mol L-1min-1
→ Average Rate : The change in concentration of reactant or product present in a chemical reaction per unit time is called average rate of reaction.
→ Instantaneous Rate : The actual rate of reaction at any time is called instantaneous rate.
→ Temperature Coefficient : The ratio of rate constants of reaction at 25°C and 35°C temperature or difference of 10°C temperature is called temperature coefficient. Its value is approximate 2 to 3.
→ Rate Law or Rate Expression : The equation which establishes relationship between rate of rection and concentration of reactants, is called rate law.
For example: aA + bB → cC + dD
According to rate law for reaction,
Reaction rate (r) = k[A]a [B]b
→ Molecularity of Reaction : The total number of molecules of reactants taking part in elementary step of reaction is called molecularity of reaction.
Simple Reactions : The reactions whose molecularity is equal to number of reactants, are called simple reactions.
Example :
→ Complex Reactions : The reactions, in which number of reactants is more than three, takes place generally in two or more steps. The slowest step in these reactions is called rate determining step. These reactions are called complex reactions. For example: HBr + O2 → 2H2O + 2Br2
Rate = k (HBr] [O2]
→ Order of Reaction : The number of reactant molecules taking part in a reaction which shows measurable change in concentration and determines the rate of reaction, is called order of reaction or the sum of power of concentration of reactants in rate law expression is known as order of reaction.
→ Half-life Period : The time required to change the half part of reactant in to product in a reaction is called half-life period (t1/2) of that reaction.
→ Pseudo Unimolecular Reactions : The reactions whose molecularity is two or more but order is one, are called pseudo unimolecular reactions, For example:
→ Activation Energy : The minimum extra amount of energy which is essentially provided to molecules for effective callision is called activation energy.
Ea = ET – ER
Where, Ea = Activation energy
ET = Threshold energy
ER = Average energy of reactants
→ Collision Frequency : The number of collisions taking place in a reaction mixture per unit volume per second is called collision frequency.
Chemistry Notes
Electrochemistry Chemistry Notes
Electrochemistry Chemistry Notes
Introduction :
→ 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.
Chemistry Notes
Solution Chemistry Notes
Solution Chemistry Notes
→ The homogeneous mixture of two or more than two components is called solution. The composition and properties are similar throughout the mixture. The properties of components are available in solution. The solution made up of two components is called binary solution.
→ Similarly, the solutions made up of three and four components are called ternary and quaternary solution respectively
- Solvents : The component which is present in large amount in solution, is called solvent. It determines the physical state of solution in which solution exists. 60% aqueous sugаr solution-water as solvent
- Solute : The component which is present in less amount, is called solute. These may also be one or more in solution
Chemistry Notes
Solid State Chemistry Notes
Solid State Chemistry Notes
- The state of matter in which constituent particles such as molecules, atoms or ions are closely packed due to strong inter molecular forces of attraction is called solid state.
- The position of constituent particles are fixed in solids. They oscillate about their mean positions only.
- In the solids, constituent particles are so closely packed by strong intermolecular forces of attraction that these remain in a nearly fixed position.
- This is the reason that both shape and volume of solids are definite.
We can define the solids as follows:
“Solid state of any substance is that state whose melting point is higher than room temperature at atmospheric pressure”.