Entropy can be defined in several ways and thus can be applied in various stages or instances, such as in a thermodynamic stage, cosmology, and even in economics.
The concept of entropy basically talks about the spontaneous changes that occur in everyday phenomena or the tendency of the universe towards disorder.
Apart from being just a scientific concept, entropy is often described as a measurable physical property that is most commonly associated with uncertainty.
Table of Contents
What Is Entropy?
Generally, entropy is defined as a measure of randomness or disorder of a system. This concept was introduced by a German physicist named Rudolf Clausius in the year 1850.
Entropy is a measure of molecular disorder.
Properties of Entropy
It is a thermodynamic function.
It is a state function. It depends on the state of the system and not the path that is followed.
It is represented by S, but in the standard state, it is represented by S°.
Its SI unit is J/Kmol.
Its CGS unit is cal/Kmol.
Entropy is an extensive property which means that it scales with the size or extent of a system.
Note: The greater disorder will be seen in an isolated system; hence, entropy also increases.
When chemical reactions take place, if reactants break into more products, entropy also gets increased.
A system at higher temperatures has greater randomness than a system at a lower temperature.
From these examples, it is clear that entropy increases with a decrease in regularity.
Entropy order : gas > liquid > solids
Entropy Change and Calculations
During entropy change, a process is defined as the amount of heat emitted or absorbed isothermally and reversibly divided by the absolute temperature. The entropy formula is given as follows:
∆S = qrev,iso/T
If we add the same quantity of heat at a higher temperature and a lower temperature, randomness will be maximum at a lower temperature. Hence, it suggests that temperature is inversely proportional to entropy.
Total entropy change, ∆Stotal =∆Ssurroundings+∆Ssystem
Total entropy change is equal to the sum of the entropy change of the system and surroundings.
If the system loses an amount of heat q at a temperature T1, which is received by surroundings at a temperature T2.
So, ∆Stotal can be calculated
∆Ssystem=-q/T1
∆Ssurrounding =q/T2
∆Stotal=-q/T1+q/T2
● If ∆Stotal is positive, the process is spontaneous.
● If ∆Stotal is negative, the process is non-spontaneous.
● If ∆Stotal is zero, the process is at equilibrium.
Points to Remember : A spontaneous process is thermodynamically irreversible. The irreversible process will attain equilibrium after some time.
Entropy change during the isothermal reversible expansion of an ideal gas
∆S = qrev,iso/T
According to the first law of thermodynamics,
∆U = q + w
For the isothermal expansion of an ideal gas, ∆U = 0
qrev = -wrev = nRT ln(V2/V1)
Therefore,
∆S = nR ln(V2/V1)
∆S = 2.303 nR log10(V2/V1)
Entropy Change During Reversible Adiabatic Expansion
For an adiabatic process, heat exchange will be zero(q = 0); therefore, reversible adiabatic expansion is taking place at a constant entropy (isentropic),
q = 0
Therefore, ∆S = 0
Even though the reversible adiabatic expansion is isentropic, the irreversible adiabatic expansion is not isentropic.
∆S is not equal to zero.
Entropy and Thermodynamics
Here, we will compare or understand the relationship between entropy and the different laws of thermodynamics.
First Law of Thermodynamics
It states that heat is a form of energy, and thermodynamic processes are, therefore, subject to the principle of conservation of energy. This means that heat energy cannot be created or destroyed. It can, however, be transferred from one place to another and converted to and from other forms of energy.
Note:
Entropy increases when solid changes to a liquid and a liquid changes into gases.
Entropy also increases when the number of moles of gaseous products increases more than the reactants.
Some things are contrary to expectations about entropy.
A hard-boiled egg has greater entropy than an unboiled egg. It is due to the denaturation of the secondary structure of the protein (albumin). Protein changes from the helical structure into a randomly coiled form.
If we stretch a rubber band, entropy gets decreased because macromolecules get uncoiled and arranged in a more ordered manner. Therefore, randomness will decrease.
Second Law of Thermodynamics
According to the concepts of entropy and spontaneity, the second law of thermodynamics has a number of definitions.
All naturally occurring spontaneous processes are thermodynamically irreversible.
Complete transmission of heat into work is thermodynamically not feasible without the wastage of a certain amount of energy.
The entropy of the universe is continuously increasing.
Total entropy change is always positive. The entropy of a system plus the entropy of its surroundings will be greater than zero.
∆Stotal = ∆Ssurroundings + ∆Ssystem > 0
Third Law of Thermodynamics
The entropy of any crystalline solid approaches zero as the temperature approaches absolute temperature. It is because there is a perfect order in a crystal at absolute zero.
The limitation of this law is that many solids do not have zero entropy at absolute zero.
For example, a glassy solid and a solid containing a mixture of isotopes.
Entropy Changes During Phase Transition
Entropy of Fusion
It is the increase in entropy when a solid melt into liquid. The entropy increases as the freedom of movement of molecules increases with phase change.
The entropy of fusion is equal to the enthalpy of fusion divided by the melting point (fusion temperature)
∆fusS=∆fusH / Tf
A natural process such as a phase transition (for example, fusion) will occur when the associated change in the Gibbs free energy is negative.
Most of the time, ∆fusS is positive
Exception
Helium-3 has a negative entropy of fusion at temperatures below 0.3 K. Helium-4 also has a very slightly negative entropy of fusion below 0.8 K.
Entropy of Vaporisation
The entropy of vaporisation is a state when there is an increase in entropy as liquid changes into a vapour. This is due to an increase in molecular movement which creates a randomness of motion.
The entropy of vaporisation is equal to the enthalpy of vaporisation divided by boiling point. It can be represented as,
∆vapS=∆vapH / Tb
Standard Entropy of Formation of a Compound
It is the entropy change that takes place when one mole of a compound in the standard state is formed from the elements in the standard state.
Spontaneity
● Exothermic reactions are spontaneous because ∆Ssurrounding is positive, which makes ∆Stotal positive.
● Endothermic reactions are spontaneous because ∆Ssystem is positive and ∆Ssurroundings is negative, but overall ∆Stotal is positive.
● Free energy change criteria for predicting spontaneity is better than entropy change criteria because the former requires only free energy change of the system, whereas the latter needs entropy change of both system and surroundings.
Negentropy
It is the reverse of entropy. It means things becoming more in order. By ‘order’, it means organisation, structure and function. It is the opposite of randomness or chaos.
One example of negentropy is a star system such as a solar system.
Solved Questions
1. The entropy of an isolated system can never ____.
a) increase
b) decrease
c) be zero
d) none of the mentioned
Answer: b
Explanation: The entropy of an isolated system always increases and remains constant only when the process is reversible.
2. According to the entropy principle, the entropy of an isolated system can never decrease and remains constant only when the process is reversible.
a) true
b) false
Answer: a
Explanation: This is the statement for the principle of increase of entropy.
3. Entropy may decrease locally in some regions within the isolated system. How can this statement be justified?
a) This cannot be possible.
b) This is possible because the entropy of an isolated system can decrease.
c) It must be compensated by a greater increase of entropy somewhere within the system.
d) None of the above.
Answer: c
Explanation: The net effect of an irreversible process is an entropy increase in the whole system.
4. Clausius summarised the first and second laws of thermodynamics as _____.
a) the energy of the world is constant
b) the entropy of the world tends towards a maximum
c) both of the above
d) none of the above
Answer: c
Explanation: These two statements were given by Clausius.
5. The entropy of an isolated system always ____ and becomes a ____ at the state of equilibrium.
a) decreases, minimum
b) increases, maximum
c) increases, minimum
d) decreases, maximum
Answer: b
Explanation: If the entropy of an isolated system varies with some parameter, then there is a certain value of that parameter that maximises the entropy.
Entropy as Disorder
Even though there are many new and different interpretations of entropy, in general, it is defined as a measure of disorder and chaos. Chaos, as such, is the state of a physical or dynamic system wherein elements of all types are mixed evenly throughout the space, and so it becomes homogeneous.
Frequently Asked Questions
Q1
Why is entropy constant at the triple point of water?
The triple point defines a situation of simultaneous equilibrium between the solid, liquid and gas phases. The entropy of the gas phase is higher than the entropy of the liquid phase.
Q2
Does freezing increase entropy?
Water has a greater entropy than ice, and so entropy favours melting. Freezing is an exothermic process; energy is lost from the water and dissipated to the surroundings. Therefore, as the surroundings get hotter, they gain more energy, and thus the entropy of the surroundings increases.
Q3
Can entropy ever decrease?
It just says that the total entropy of the universe can never decrease. Entropy can decrease somewhere, provided it increases somewhere else by at least as much. The entropy of a system decreases only when it interacts with some other system whose entropy increases in the process. That is the law.
Q4
Can entropy be infinite?
Since no finite system can have an infinite number of microstates, it’s impossible for the entropy of the system to be infinite. In fact, entropy tends towards finite maximum values as a system approaches equilibrium.
Q5
Can entropy be negative?
If entropy is the amount of disorder, negative entropy means something has less disorder or more order. The shirt is now less disordered and in a state of negative entropy, but you are more disordered and thus, the system as a whole is in a state of either zero entropy or positive entropy.
Q6
What causes entropy?
Several factors affect the amount of entropy in a system. If you increase temperature, you increase entropy.
More energy put into a system excites the molecules and the amount of random activity.
As the gas expands in a system, entropy increases.
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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