The equilibrium constant of a chemical reaction (usually denoted by the symbol K) provides insight into the relationship between the products and reactants when a chemical reaction reaches equilibrium.
For example, the equilibrium constant of concentration (denoted by Kc) of a chemical reaction at equilibrium can be defined as the ratio of the concentration of products to the concentration of the reactants, each raised to their respective stoichiometric coefficients. I
t is important to note that there are different types of equilibrium constants that provide relationships between the products and the reactants of equilibrium reactions in terms of different units.
For a chemical reaction, the equilibrium constant can be defined as the ratio between the amount of reactant and the amount of product which is used to determine chemical behaviour.
At equilibrium, the rate of the forward reaction = rate of the backward reaction
At a particular temperature, the rate constants are constant. The ratio of the rate constant of forward reaction to the rate constant of backward reaction should be a constant and is called an equilibrium constant (Kequ).
Equilibrium Constant Formula
Kequ = kf/kb = [C]c [D]d/[A]a [B]b = Kc
Where Kc indicates the equilibrium constant measured in moles per litre.
For reactions involving gases: The equilibrium constant formula, in terms of partial pressure, will be:
Kequ = kf/kb = [[pC]c [pD]d]/[[pA]a [pB]b] = Kp
Where Kp indicates the equilibrium constant formula in terms of partial pressures.
Medium Kc/Kp values indicate optimum product formation.
Table of Contents
Units of Equilibrium Constant
The equilibrium constant is the ratio of the concentrations raised to the stoichiometric coefficients. Therefore, the unit of the equilibrium constant = [Mole L-1]△n.
Where, ∆n = sum of stoichiometric coefficients of products – sum of stoichiometric coefficients of reactants.
Equilibrium Constant, Reaction Quotient and Gibbs Free Energy
K is the ratio of the relative amount of products to reactants at equilibrium, while Q is the ratio at any point in time of the reaction. The Q value can be compared to K to determine the direction of the reaction to take place. The spontaneity of the process is related to the free energy change. △G (Gibbs Free Energy), K (Equilibrium Constant), and Q (Reaction Quotient) are related, as detailed below:
△G < 0 and Qc ˂ Kc or Kp at the start of the reaction: The reaction will proceed to form products.
△G = 0 and Qc = Kc or Kp at equilibrium, and no more changes in the concentration of the mixture.
△G > 0 and Qc > Kc or Kp after equilibrium: The reaction will proceed in the direction to form reactants.
Equilibrium Constant vs Reaction Quotient
Kc = Equilibrium constant measured in moles per litre.
Kp = Equilibrium constant calculated from the partial pressures
Relationship between kc and kp
Consider the following reversible reaction:
cC + dD ⇒ aA + bB
The equilibrium constant for the reaction is expressed in terms of the concentration (mole/litre):
If the equilibrium involves gaseous species, then the concentrations are replaced by partial pressures of the gaseous substances. The equilibrium constant in terms of partial pressures is:
Where pA, pB, pC and pD represent the partial pressures of the substance A, B, C and D, respectively. If gases are assumed to be ideal, then according to the ideal gas equation:
pV = nRT or p = nRT/V
Where,
p is the pressure in Pa
n is the number of moles of gas
V is the volume in m3
T is the temperature in Kelvin
n/V = molar concentration = [C]
If C is in mol dm3 and p is in bar, then R = 0.0831 bar dm3 mol-1 K-1 or p = CRT
Substituting for pressure, in terms of concentration:
pA = [A] RT; pB = [B] RT; pC = [C] RT and pD = [D] RT
i.e. number of moles of gaseous products – number of moles of gaseous reactants in the balanced chemical reaction.
Characteristics of Equilibrium Constant
It is reaction specific, and at a constant temperature, it is fixed.
A catalyst changes the rate of forward and backward reactions equally, not to affect the value of the equilibrium constant.
Changes in concentration, pressure, temperature, and inert gases may affect the equilibrium, favouring either forward or backward reaction but not the equilibrium constant.
It is related to the standard free energy as, △G0= -RT ln Kequ.
For the same reversible reaction, Kequ has different values at different temperatures.
The equilibrium constant of the reverse equilibrium is the reciprocal of the original equilibrium, i.e. Krev = 1/Kequ.
If the equilibrium reaction stoichiometry is changed, the power of the equilibrium constant also gets changed by the same quantity.
If the equilibrium constant for the reaction, A + B ⇌ C + D, is K, then, for equilibrium reaction 3A = 3B ⇒ 3C + 3D is K3.
In case the stepwise multiple equilibria lead to the final products, the equilibrium constant of the net equilibrium = product of each stepwise equilibrium constant. Therefore, the net equilibrium constant K = K1 × K2 × K3.
Simultaneous equilibrium reactions have a common product. The equilibrium constant of the reactions does not change. Due to the higher concentration of the common product, the product concentrations will be reduced.
Applications of Equilibrium Constant
Equilibrium Constant for Predicting the Extent of Reaction
The equilibrium constant (Kc) can be used to predict the extent of a reaction, i.e. the degree of the disappearance of the reactants. The magnitude of the equilibrium constant gives an idea of the relative amount of the reactants and the products.
Case 1: The larger value of the equilibrium constant (>103) shows that forward reaction is favoured, i.e. the concentration of products is much larger than that of the reactants at equilibrium.
For example,
H2(g) + Br2(g)⇌ 2HBr(g) ⇒ Kc = 5.4×1018
H2(g) + Cl2(g)⇌ 2HCl(g) ⇒ Kc = 4×1031
H2(g) + 12O2(g) ⇌ H2O(g) ⇒ Kc = 2.4×1047
This shows that at equilibrium, the concentration of the products is very high, i.e. reaction goes almost to completion.
Case 2: Intermediate value of the equilibrium constant (10-3 to 103) show that the concentration of the reactants and products are comparable.
For example,
Fe3 (aq) + SCN (aq) ⇌ [Fe(SCN)]2 (aq) ⇒ Kc = 138 at 298 K
H2 (g) + I2 (g) ⇌ 2HI (g) ⇒ Kc = 57 at 700 K.
Case 3: Low value of equilibrium constant (<10-3) shows that backward reaction is favoured, i.e. concentration of reactants is much larger than that of products, i.e. the reaction proceeds to a very small extent in the forward direction.
Equilibrium Constant for Predicting the Direction of a Reaction
The equilibrium constant can be used to predict the direction of the reaction. We need a term, reaction quotient (Qc expressed in terms of concentrations or Qp in terms of partial pressures) similar to the equilibrium constant, except that the conditions are not at equilibrium.
For a balanced reaction, aA + bB ⇌ cC + dD
The reaction quotient (Qc or Qp) is given as:
Qc = [C]c[D]d/[A]a[B]b
Qp = pcC × pdD / paA × pbB
Comparison with Kc and the direction of reaction:
If Q = Kc, the reaction is in equilibrium [Where, Kc = equilibrium constant]
If Q > Kc, Q tends to decrease so as to become equal to K, the reaction will proceed in the backward direction.
If Q < Kc, Q tends to increase so as to become equal to K, the reaction will proceed in the forward direction.
Calculating the Equilibrium Concentration
1. From Equilibrium Constant:
The degree of dissociation of an equilibrium involving gas can be calculated by knowing the equilibrium constant and the concentration of the gaseous reactant/product.
For example, in the decomposition of carbonate, the number of moles of carbon dioxide can be calculated from the equilibrium constant by assuming an ideal gas behaviour.
CaCO3 ⇌ CaO + CO2 Kp = [pco2]
The decomposition of ammonia gas is given below:
Decomposition of Ammonia Reaction: 2NH3 ⇌ N2 + 3H2
For initial moles
1
0
0
Moles at equilibrium
1−2α
α
3α
For C moles at equilibrium
C(1−2α)
Cα
3Cα
Number of moles at equilibrium = C(1 – 2α) + Cα + 3Cα = C(1 + 2α)
Partial pressure of ammonia = C(1 – 2α) /C(1 + 2α) = [(1 – 2α)/(1+2α)] Pt (Pt is the total presure)
By knowing Kp and the total pressure, the degree of dissociation of ammonia can be calculated.
2. From Vapour Density Measurements
Vapour Density and Number of Moles:
For ideal gases, pV =nRT = [ω/M] × RT
M = [ωRT]/VP = ρ [RT]/P = ρ[RTV]/RTn = ρ V/n = 2 × Vapour Density
Vapour density = ρ × V/2n = α × 1/n
At equilibrium, V and ρ are constant, and Vapour Density is α × 1/n
Vapour Density and Equilibrium:
Vapour density at start/vapour density at equilibrium = D/d = M/m = Moles at equilibrium/Moles at start.
M = initial molecular weight and m = molecular weight at equilibrium
For example,
Reaction: PCl5 ⇌ PCl3 + Cl2
For initial moles
C
0
0
Moles at equilibrium
C(1 – α)
Cα
Cα
Number of moles at equilibrium = C (1 – α) + Cα + Cα = C (1 + α)
C (1 + α) C = D/d : 1 + α
α = D/d – 1
Knowing D and d, or M and m, α can be calculated.
Factors Affecting Equilibrium Constant
Some factors that affect the equilibrium constant are as follows:
Change in concentration of any product or reactant.
Change in the pressure of the system.
Change in temperature of the system.
Adding inert gas.
Adding catalyst.
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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