When the concentrations of reactants and products do not change over time, they are said to be in a state of equilibrium. The stability of certain observable attributes such as pressure, density, and so on can be used to identify this state.
Physical equilibrium is the equilibrium set up in physical processes. Chemical equilibrium is the state of being in equilibrium in a chemical process.
The temperature, pressure, and concentration of the system are all factors that affect equilibrium. When one of these factors changes, the equilibrium of the system is disrupted, and the system readjusts itself until it returns to equilibrium. The following sections go through some of the most essential aspects that impact equilibria.
Table of Contents
Chemical Equilibrium
Chemical equilibrium is the state of a system in which the concentration of the reactant and the concentration of the products do not change over time and the system’s properties do not change. When the rate of the forward reaction equals the rate of the reverse reaction, the system reaches chemical equilibrium.
In chemical equilibrium, the rate of the forward reaction is equal to the rate of the backward reaction. so it refers to the state of a system in which the reactant and product concentrations do not fluctuate over time.
The system’s properties will no longer vary after that, and it will become constant. The system is considered to be in a state of dynamic equilibrium when the concentrations of the reactants and products do not vary due to equal rates of the forward and reverse reactions.
French chemists Le-Chatelier and Braun proposed certain generalizations to explain the influence of changes in temperature, concentration, or pressure on the state of an equilibrium system. When one of these parameters changes, the equilibrium of the system is disrupted, and the system readjusts itself until it returns to equilibrium. Le-Chatelier Principle is the name of the generalization.
Le-Chatelier’s principle might be described as: ”a change in any of the components that determine a system’s equilibrium conditions will move the equilibrium in such a way that the effect of the change is reduced or counteracted”.
The principle is extremely useful for qualitatively forecasting the effect of a change in concentration, pressure, or temperature on an equilibrium system. Both chemical and physical equilibrium is governed by this principle. The temperature, pressure, and concentration of the system are all factors that affect equilibrium. The following section goes through some of the most essential factors that affect equilibria.
Change in Concentration
When the concentration of any of the reactants or products in an equilibrium reaction is altered, the equilibrium mixture’s composition changes in order to minimize the effect of the concentration change. According to the Le-Chatelier principle,
The reaction that consumes the substance that is added, reduces the concentration of the reactants or products added.
The reaction in the direction that replenishes the substance that is withdrawn reduces the concentration of reactants or products removed.
It may be concluded that increasing the concentration of one or all of the reactant species causes the equilibrium to shift forward, resulting in the formation of more products. When the concentration of one or more of the product species is increased, the equilibrium moves backwards, resulting in the formation of more reactants. So, the composition of the mixture in chemical equilibrium changes when the concentration of the reactant or product is changed.
Change in Temperature
According to Le-Chatelier’s principle if the temperature of an equilibrium system is increased, i.e., when heat is supplied, the equilibrium will move in the direction of the added heat. With an increase in temperature, the equilibrium will move in the direction of an endothermic reaction. The decrease in temperature, on the other hand, will shift the equilibrium in the direction of heat production, favoring exothermic reactions. The effect of temperature on chemical equilibrium is determined by the reaction’s sign of ΔH, according to Le-Chatelier’s principle.
As the temperature increases, the equilibrium constant of an exothermic reaction decreases.
The equilibrium constant of an endothermic reaction increases as the temperature increases.
The rate of reaction is affected by temperature changes in addition to the equilibrium constant.
Change in Pressure
The volume changes, which causes a change in pressure. Since the total number of gaseous reactants and products is now different, a change in pressure can impact the gaseous reaction. The pressure has no effect on the equilibrium if the number of moles of gaseous reactants and products does not change. The change in pressure in both liquids and solids can be neglected in heterogeneous chemical equilibrium, according to Le- Chatelier’s principle, because the volume of a solution is virtually independent of pressure. As a result, the change in volume affects the equilibrium in the following way:
When the pressure is increased, the reaction reverses because the number of moles of gas on the reactant’s side is decreased.
When the pressure is reduced, the reaction proceeds forward because the number of moles of gas on the product’s side is reduced.
Change in Volume
Since an increase in pressure results in a decrease in volume, the effect of a change in volume will be exactly the opposite of that of a change in pressure. As a result, the change in volume has the following effect on the equilibrium:
When the volume of a gaseous mixture at equilibrium is reduced, the equilibrium moves in the direction of a smaller number of gaseous molecules.
When the volume of a gaseous mixture at equilibrium is increased, the equilibrium moves in the direction of a larger number of gaseous molecules.
Effect of a Catalyst
The equilibrium is unaffected by the catalyst. This is due to the fact that the catalyst favours both forward and backward reactions equally. As a result, the forward-to-reverse rate ratio remains unchanged, and there is no net change in the relative number of reactants and products present at equilibrium. Thus, a catalyst has no effect on the equilibrium position.
As a result, a catalyst has no impact on the chemical equilibrium. It simply accelerates a reaction. A catalyst, in general, speeds up both forward and reverse reactions. Thus, the reaction reaches equilibrium more quickly.
In a catalyzed or non-catalyzed reaction, the same number of reactants and products will be present at equilibrium. The presence of a catalyst simply aids the reaction by allowing it to progress through a lower-energy transition state of reactants to products.
Effect of Addition of an Inert Gas
Depending on the conditions, adding inert gas to the equilibrium has the following effects.
Addition of inert gas at constant volume- When a constant volume of inert gas is added to the equilibrium system, the total pressure increases. The concentrations of the reactants and products, on the other hand, will remain unchanged. As a result, there will be no effect on the equilibrium under these conditions.
Addition of inert gas at constant pressure- When at constant pressure, an inert gas is added to the equilibrium system, the volume increases. As a result, the number of moles per unit volume of various reactants and products will decrease. So, the equilibrium will shift in favour of an increase in the number of moles of gases.
Solved Problems
Question 1: At 27°C and 127°C, the reaction equilibrium constants are 1.6×10-3 and 7.6×10-2, respectively. Is this an endothermic or exothermic reaction?
Answer:
An endothermic reaction’s equilibrium constant increases as the temperature increases. Given that the equilibrium constants have increased with temperature from 1.6×10-3 to 7.6×10-2, so the reaction is endothermic in the forward direction.
Question 2: What is the significance of the term “Dynamic Equilibrium” for chemical equilibrium?
Answer:
An equilibrium stage is defined as the stage where the rate of the forward response equals the rate of backward reaction. The number of reactant molecules converting to products and product molecules converting to reactants is the same at this point. Chemical equilibrium is dynamic because the same equilibrium can be achieved with the same reactants in identical conditions anywhere with continuous molecule exchange.
Question 3: When the equilibrium is reached, what happens to the forward and backward reaction rates?
Answer:
When equilibrium is reached, the rate of the forward reaction equals the rate of the backward reaction.
Question 4: Which direction will the equilibrium reaction shift in the presence of a catalyst?
Answer:
The rate of the forward and backward reactions is equally favored by a catalyst. As a result, the presence of a catalyst has no effect on the equilibrium.
Question 5: If the temperature of the following reaction is raised, which direction will the equilibrium shift?
N2O4(g) ⇌ 2NO2(g) ΔH=+57.2
Answer:
This process is endothermic since the given heat of reaction is positive. So, increasing the temperature, according to Le Chatelier’s principle, will shift the equilibrium to the right, producing more NO2.
Neeraj Anand, Param Anand
Er. Neeraj K.Anand is a freelance mentor and writer who specializes in Engineering & Science subjects. Neeraj Anand received a B.Tech degree in Electronics and Communication Engineering from N.I.T Warangal & M.Tech Post Graduation from IETE, New Delhi. He has over 30 years of teaching experience and serves as the Head of Department of ANAND CLASSES. He concentrated all his energy and experiences in academics and subsequently grew up as one of the best mentors in the country for students aspiring for success in competitive examinations.
In parallel, he started a Technical Publication "ANAND TECHNICAL PUBLISHERS" in 2002 and Educational Newspaper "NATIONAL EDUCATION NEWS" in 2014 at Jalandhar. Now he is a Director of leading publication "ANAND TECHNICAL PUBLISHERS", "ANAND CLASSES" and "NATIONAL EDUCATION NEWS".
He has published more than hundred books in the field of Physics, Mathematics, Computers and Information Technology. Besides this he has written many books to help students prepare for IIT-JEE and AIPMT entrance exams. He is an executive member of the IEEE (Institute of Electrical & Electronics Engineers. USA) and honorary member of many Indian scientific societies such as Institution of Electronics & Telecommunication Engineers, Aeronautical Society of India, Bioinformatics Institute of India, Institution of Engineers. He has got award from American Biographical Institute Board of International Research in the year 2005.
CBSE Class 11 Chemistry Syllabus is a vast which needs a clear understanding of the concepts and topics. Knowing CBSE Class 11 Chemistry syllabus helps students to understand the course structure of Chemistry.
Unit-wise CBSE Class 11 Syllabus for Chemistry
Below is a list of detailed information on each unit for Class 11 Students.
UNIT I – Some Basic Concepts of Chemistry
General Introduction: Importance and scope of Chemistry.
Nature of matter, laws of chemical combination, Dalton’s atomic theory: concept of elements, atoms and molecules.
Atomic and molecular masses, mole concept and molar mass, percentage composition, empirical and molecular formula, chemical reactions, stoichiometry and calculations based on stoichiometry.
UNIT II – Structure of Atom
Discovery of Electron, Proton and Neutron, atomic number, isotopes and isobars. Thomson’s model and its limitations. Rutherford’s model and its limitations, Bohr’s model and its limitations, concept of shells and subshells, dual nature of matter and light, de Broglie’s relationship, Heisenberg uncertainty principle, concept of orbitals, quantum numbers, shapes of s, p and d orbitals, rules for filling electrons in orbitals – Aufbau principle, Pauli’s exclusion principle and Hund’s rule, electronic configuration of atoms, stability of half-filled and completely filled orbitals.
UNIT III – Classification of Elements and Periodicity in Properties
Significance of classification, brief history of the development of periodic table, modern periodic law and the present form of periodic table, periodic trends in properties of elements -atomic radii, ionic radii, inert gas radii, Ionization enthalpy, electron gain enthalpy, electronegativity, valency. Nomenclature of elements with atomic number greater than 100.
UNIT IV – Chemical Bonding and Molecular Structure
Valence electrons, ionic bond, covalent bond, bond parameters, Lewis structure, polar character of covalent bond, covalent character of ionic bond, valence bond theory, resonance, geometry of covalent molecules, VSEPR theory, concept of hybridization, involving s, p and d orbitals and shapes of some simple molecules, molecular orbital theory of homonuclear diatomic molecules(qualitative idea only), Hydrogen bond.
UNIT V – Chemical Thermodynamics
Concepts of System and types of systems, surroundings, work, heat, energy, extensive and intensive properties, state functions. First law of thermodynamics – internal energy and enthalpy, measurement of U and H, Hess’s law of constant heat summation, enthalpy of bond dissociation, combustion, formation, atomization, sublimation, phase transition, ionization, solution and dilution. Second law of Thermodynamics (brief introduction) Introduction of entropy as a state function, Gibb’s energy change for spontaneous and nonspontaneous processes. Third law of thermodynamics (brief introduction).
UNIT VI – Equilibrium
Equilibrium in physical and chemical processes, dynamic nature of equilibrium, law of mass action, equilibrium constant, factors affecting equilibrium – Le Chatelier’s principle, ionic equilibrium- ionization of acids and bases, strong and weak electrolytes, degree of ionization, ionization of poly basic acids, acid strength, concept of pH, hydrolysis of salts (elementary idea), buffer solution, Henderson Equation, solubility product, common ion effect (with illustrative examples).
UNIT VII – Redox Reactions
Concept of oxidation and reduction, redox reactions, oxidation number, balancing redox reactions, in terms of loss and gain of electrons and change in oxidation number, applications of redox reactions.
UNIT VIII – Organic Chemistry: Some basic Principles and Techniques
General introduction, classification and IUPAC nomenclature of organic compounds. Electronic displacements in a covalent bond: inductive effect, electromeric effect, resonance and hyper conjugation. Homolytic and heterolytic fission of a covalent bond: free radicals, carbocations, carbanions, electrophiles and nucleophiles, types of organic reactions.
UNIT IX – Hydrocarbons
Classification of Hydrocarbons Aliphatic Hydrocarbons: Alkanes – Nomenclature, isomerism, conformation (ethane only), physical properties, chemical reactions. Alkenes – Nomenclature, structure of double bond (ethene), geometrical isomerism, physical properties, methods of preparation, chemical reactions: addition of hydrogen, halogen, water, hydrogen halides (Markovnikov’s addition and peroxide effect), ozonolysis, oxidation, mechanism of electrophilic addition. Alkynes – Nomenclature, structure of triple bond (ethyne), physical properties, methods of preparation, chemical reactions: acidic character of alkynes, addition reaction of – hydrogen, halogens, hydrogen halides and water.
Aromatic Hydrocarbons:
Introduction, IUPAC nomenclature, benzene: resonance, aromaticity, chemical properties: mechanism of electrophilic substitution. Nitration, sulphonation, halogenation, Friedel Craft’s alkylation and acylation, directive influence of functional group in monosubstituted benzene. Carcinogenicity and toxicity.
To know the CBSE Syllabus for all the classes from 1 to 12, visit the Syllabus page of CBSE. Meanwhile, to get the Practical Syllabus of Class 11 Chemistry, read on to find out more about the syllabus and related information in this page.
CBSE Class 11 Chemistry Practical Syllabus with Marking Scheme
In Chemistry subject, practical also plays a vital role in improving their academic scores in the subject. The overall weightage of Chemistry practical mentioned in the CBSE Class 11 Chemistry syllabus is 30 marks. So, students must try their best to score well in practicals along with theory. It will help in increasing their overall academic score.
CBSE Class 11 Chemistry Practical Syllabus
The experiments will be conducted under the supervision of subject teacher. CBSE Chemistry Practicals is for 30 marks. This contribute to the overall practical marks for the subject.
The table below consists of evaluation scheme of practical exams.
Evaluation Scheme
Marks
Volumetric Analysis
08
Salt Analysis
08
Content Based Experiment
06
Project Work
04
Class record and viva
04
Total
30
CBSE Syllabus for Class 11 Chemistry Practical
Micro-chemical methods are available for several of the practical experiments. Wherever possible such techniques should be used.
A. Basic Laboratory Techniques 1. Cutting glass tube and glass rod 2. Bending a glass tube 3. Drawing out a glass jet 4. Boring a cork
B. Characterization and Purification of Chemical Substances 1. Determination of melting point of an organic compound. 2. Determination of boiling point of an organic compound. 3. Crystallization of impure sample of any one of the following: Alum, Copper Sulphate, Benzoic Acid.
C. Experiments based on pH
1. Any one of the following experiments:
Determination of pH of some solutions obtained from fruit juices, solution of known and varied concentrations of acids, bases and salts using pH paper or universal indicator.
Comparing the pH of solutions of strong and weak acids of same concentration.
Study the pH change in the titration of a strong base using universal indicator.
2. Study the pH change by common-ion in case of weak acids and weak bases.
D. Chemical Equilibrium One of the following experiments:
1. Study the shift in equilibrium between ferric ions and thiocyanate ions by increasing/decreasing the concentration of either of the ions. 2. Study the shift in equilibrium between [Co(H2O)6] 2+ and chloride ions by changing the concentration of either of the ions.
E. Quantitative Estimation i. Using a mechanical balance/electronic balance. ii. Preparation of standard solution of Oxalic acid. iii. Determination of strength of a given solution of Sodium hydroxide by titrating it against standard solution of Oxalic acid. iv. Preparation of standard solution of Sodium carbonate. v. Determination of strength of a given solution of hydrochloric acid by titrating it against standard Sodium Carbonatesolution.
F. Qualitative Analysis 1) Determination of one anion and one cation in a given salt Cations‐ Pb2+, Cu2+, As3+, Al3+, Fe3+, Mn2+, Ni2+, Zn2+, Co2+, Ca2+, Sr2+, Ba2+, Mg2+, NH4+ Anions – (CO3)2‐ , S2‐, NO2‐ , SO32‐, SO2‐ , NO ‐ , Cl‐ , Br‐, I‐, PO43‐ , C2O2‐ ,CH3COO‐ (Note: Insoluble salts excluded)
2) Detection of ‐ Nitrogen, Sulphur, Chlorine in organic compounds.
G) PROJECTS Scientific investigations involving laboratory testing and collecting information from other sources.
A few suggested projects are as follows:
Checking the bacterial contamination in drinking water by testing sulphide ion
Study of the methods of purification of water.
Testing the hardness, presence of Iron, Fluoride, Chloride, etc., depending upon the regional variation in drinking water and study of causes of presence of these ions above permissible limit (if any).
Investigation of the foaming capacity of different washing soaps and the effect of addition of Sodium carbonate on it.
Study the acidity of different samples of tea leaves.
Determination of the rate of evaporation of different liquids Study the effect of acids and bases on the tensile strength of fibres.
Study of acidity of fruit and vegetable juices.
Note: Any other investigatory project, which involves about 10 periods of work, can be chosen with theapproval of the teacher.
Practical Examination for Visually Impaired Students of Class 11
Below is a list of practicals for the visually impaired students.
A. List of apparatus for identification for assessment in practicals (All experiments) Beaker, tripod stand, wire gauze, glass rod, funnel, filter paper, Bunsen burner, test tube, test tube stand, dropper, test tube holder, ignition tube, china dish, tongs, standard flask, pipette, burette, conical flask, clamp stand, dropper, wash bottle • Odour detection in qualitative analysis • Procedure/Setup of the apparatus
B. List of Experiments A. Characterization and Purification of Chemical Substances 1. Crystallization of an impure sample of any one of the following: copper sulphate, benzoic acid B. Experiments based on pH 1. Determination of pH of some solutions obtained from fruit juices, solutions of known and varied concentrations of acids, bases and salts using pH paper 2. Comparing the pH of solutions of strong and weak acids of same concentration.
C. Chemical Equilibrium 1. Study the shift in equilibrium between ferric ions and thiocyanate ions by increasing/decreasing the concentration of eitherions. 2. Study the shift in equilibrium between [Co(H2O)6]2+ and chloride ions by changing the concentration of either of the ions.
D. Quantitative estimation 1. Preparation of standard solution of oxalic acid. 2. Determination of molarity of a given solution of sodium hydroxide by titrating it against standard solution of oxalic acid.
E. Qualitative Analysis 1. Determination of one anion and one cation in a given salt 2. Cations – NH+4 Anions – (CO3)2-, S2-, (SO3)2-, Cl-, CH3COO- (Note: insoluble salts excluded) 3. Detection of Nitrogen in the given organic compound. 4. Detection of Halogen in the given organic compound.
Note: The above practicals may be carried out in an experiential manner rather than recording observations.
We hope students must have found this information on CBSE Syllabus useful for their studying Chemistry. Learn Maths & Science in interactive and fun loving ways with ANAND CLASSES (A School Of Competitions) App/Tablet.
Frequently Asked Questions on CBSE Class 11 Chemistry Syllabus
Q1
How many units are in the CBSE Class 11 Chemistry Syllabus?
There are 9 units in the CBSE Class 11 Chemistry Syllabus. Students can access various study materials for the chapters mentioned in this article for free at ANAND CLASSES (A School Of Competitions).
Q2
What is the total marks for practicals examination as per the CBSE Class 11 Chemistry Syllabus?
The total marks for the practicals as per the CBSE Class 11 Chemistry Syllabus is 30. It includes volumetric analysis, content-based experiment, salt analysis, class record, project work and viva.
Q3
Which chapter carries more weightage as per the CBSE Syllabus for Class 11 Chemistry?
The organic chemistry chapter carries more weightage as per the CBSE Syllabus for Class 11 Chemistry.
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