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Lesson Posted on 06 Sep CBSE/Class 11/Science/Chemistry CBSE/Class 11/Science/Physics Exam Coaching/Engineering Entrance Coaching/IIT JEE Coaching +1 Exam Coaching/Engineering Entrance Coaching/GATE Coaching less

All about entropy

Subrat Majhi

Fine at science 10th - 10cgpa 12th 90.60% Will make u aware of how science in linked with your life at every moment

Entropy, the measure of a system s thermal energy per unit temperaturethat is unavailable for doing useful work. Because work is obtained from ordered molecular motion, the amount of entropy is also a measure of the molecular disorder, or randomness, of a system. The concept of entropy provides deep... read more

Entropy, the measure of a system?s thermal energy per unit temperaturethat is unavailable for doing useful work. Because work is obtained from ordered molecular motion, the amount of entropy is also a measure of the molecular disorder, or randomness, of a system. The concept of entropy provides deep insight into the direction of spontaneous change for many everyday phenomena. Its introduction by the German physicist Rudolf Clausius in 1850 is a highlight of 19th-century physics.

The idea of entropy provides a mathematical way to encode the intuitive notion of which processes are impossible, even though they would not violate the fundamental law of conservation of energy. For example, a block of ice placed on a hot stove surely melts, while the stove grows cooler. Such a process is called irreversible because no slight change will cause the melted water to turn back into ice while the stove grows hotter. In contrast, a block of ice placed in an ice-water bath will either thaw a little more or freeze a little more, depending on whether a small amount of heat is added to or subtracted from the system. Such a process is reversible because only an infinitesimal amount of heat is needed to change its direction from progressive freezing to progressive thawing. Similarly, compressed gasconfined in a cylinder could either expand freely into the atmosphere if a valve were opened (an irreversible process), or it could do useful work by pushing a moveable piston against the force needed to confine the gas. The latter process is reversible because only a slight increase in the restraining force could reverse the direction of the process from expansion to compression. For reversible processes the system is in equilibrium with its environment, while for irreversible processes it is not.

To provide a quantitative measure for the direction of spontaneous change, Clausius introduced the concept of entropy as a precise way of expressing the second law of thermodynamics. The Clausius form of the second law states that spontaneous change for an irreversible process in an isolated system (that is, one that does not exchange heat or work with its surroundings) always proceeds in the direction of increasing entropy. For example, the block of ice and the stove constitute two parts of an isolated system for which total entropy increases as the ice melts.

By the Clausius definition, if an amount of heat Q flows into a large heat reservoir at temperature Tabove absolute zero, then the entropy increase is ?S = Q/T. This equation effectively gives an alternate definition of temperature that agrees with the usual definition. Assume that there are two heat reservoirs R1 and R2 at temperatures T1 and T2 (such as the stove and the block of ice). If an amount of heat Qflows from R1 to R2, then the net entropy change for the two reservoirs isentropy equationwhich is positive provided that T1 > T2. Thus, the observation that heat never flows spontaneously from cold to hot is equivalent to requiring the net entropy change to be positive for a spontaneous flow of heat. If T1 = T2, then the reservoirs are in equilibrium, no heat flows, and ?S = 0.

 

The condition ?S ? 0 determines the maximum possible efficiency of heat engines?that is, systems such as gasoline or steam engines that can do work in a cyclic fashion. Suppose a heat engine absorbs heat Q1 from R1and exhausts heat Q2 to R2 for each complete cycle. By conservation of energy, the work done per cycle is W= Q1 ? Q2, and the net entropy change isentropy equationTo make W as large as possible, Q2should be as small as possible relative to Q1. However, Q2 cannot be zero, because this would make ?Snegative and so violate the second law. The smallest possible value of Q2corresponds to the condition ?S = 0, yieldingentropy equationas the fundamental equation limiting the efficiency of all heat engines. A process for which ?S = 0 is reversible because an infinitesimal change would be sufficient to make the heat engine run backward as a refrigerator.

 

The same reasoning can also determine the entropy change for the working substance in the heat engine, such as a gas in a cylinder with a movable piston. If the gas absorbs an incremental amount of heat dQ from a heat reservoir at temperature T and expands reversibly against the maximum possible restraining pressure P, then it does the maximum work dW = PdV, where dV is the change in volume. The internal energy of the gas might also change by an amount dU as it expands. Then by conservation of energy, dQ = dU + PdV. Because the net entropy change for the system plus reservoir is zero when maximum work is done and the entropy of the reservoir decreases by an amount dSreservoir = ?dQ/T, this must be counterbalanced by an entropy increase ofentropy equationfor the working gas so that dSsystem + dSreservoir = 0. For any real process, less than the maximum work would be done (because of friction, for example), and so the actual amount of heat dQ? absorbed from the heat reservoir would be less than the maximum amount dQ. For example, the gas could be allowed to expand freely into a vacuum and do no work at all. Therefore, it can be stated thatentropy equationwith dQ? = dQ in the case of maximum work corresponding to a reversible process.

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Aditi S.

If you are from ICSE or cbse board then you can read physics and chemistry at home and take tution for maths only. But if you are from West Bengal board.. you can take tution for PCM. This is because some of chapters of class 11 are introduced in cbse and icse board but not in West Bengal board.
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Sourabh Shukla

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• If you are an average student (getting 55-75% marks) or below average you need help from tuition !! • if you have chosen different streams other than SCIENCE like Arts , Commerce and you are serious about it then I recommend tuition because 11 CLASS IS GOING TO BE YOUR NURSERY for these... read more

• If you are an average student (getting 55-75% marks) or below average you need help from tuition !! 

 

• if you have chosen different streams other than SCIENCE like Arts , Commerce and you are serious about it then I recommend tuition because  11 CLASS IS GOING TO BE YOUR NURSERY for these new alien streams .

 

• If you are intelligent (Scores 80% above) you JUST need BOOKS   .

 

https://renowned-economics-tuition-ret.business.site/

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Etoos Smart Learning Center

It is just the suitable time to begin your JEE and Board exam preparation. Start studying from NCERT books. They are a pre-requisite and will build a foundation for competitive exams. Divide the number of hours you will be devoting to each topic. Remember, every subject is important so make sure you... read more

It is just the suitable time to begin your JEE and Board exam preparation. Start studying from NCERT books. They are a pre-requisite and will build a foundation for competitive exams. Divide the number of hours you will be devoting to each topic. Remember, every subject is important so make sure you don't ignore anything.  Once done with NCERT, start with revision and solve previous year questions papers. Don't forget to keep a healthy mind and body while preparing for JEE! All the best!

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Lokesh Baviskar

Yes definitely you can start preparation for IIT JEE from 12 but there are certain conditions- 1.You should follow good strategy's which involve appropriate time given test,follow good material . 2. Don't in go much detail .only learn essential.dont try to be researcher. 3.Follow only good question... read more

Yes definitely you can start preparation for IIT JEE from 12 but there are certain conditions- 

1.You should follow good strategy's which involve appropriate time given test,follow good material .

2. Don't in go much detail .only learn essential.dont try to be researcher.

3.Follow only good question set like Previous year.Sucess lies in how much time you repeat same question set.If you follow that then each time you will learn something more in that topic.Suceesively your ability to solve problems increase.

4.At last but not least be focus.all the best

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