What is Second law of thermodyanmics: Definition and 25 Discussions

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  1. C

    Work greater than heat given to colder reservoir -- impossible?

    photo below... Is it possible to make a machine that would take more heat from the hot reservoir to do work than what would hot reservoir give to the cold reservoir(heat)? Apparently, it's impossible because it violates 1st law of thermodynamics. the thickness of the arrows symbolizes the...
  2. Harikesh_33

    B Question regarding Heat Transfer in Carnot Engine

    ***A Carnot Engine*** is a theoretical engine unlike a Sterling Engine which can be made practically. Some of the drawbacks of Carnot Engine are, 1)The Heat Transfer occurs only during isothermal process(compression and expansion),this is because the working material (ie) gas or fuel used, if...
  3. S

    I Is Entropy in the Universe Lower Now Than After the Big Bang Due to Heat?

    If the universe was very hot right after the Big Bang how come the entropy of the universe was lower at that point than now? Isn't heat a reason for higher entropy?
  4. K

    I Theoretical maximum efficiency of a heat engine without Carnot

    Through an intriguing fictitious dialog between Sadi Carnot and Robert Sterling, Prof. Israel Urieli of the Ohio University shows that it is not required to invoke entropy, the second law of thermodynamics, and the Carnot cycle with the [ideal] adiabatic processes in order to find out the...
  5. Second Law of Thermodynamics and Heat Engines #11

    Second Law of Thermodynamics and Heat Engines #11

    The Second Law of Thermodynamics is not an easy topic. However, if you understand the concept of direction of thermodynamic processes and heat engines, you w...
  6. E

    Engineering Efficiency of Heat Engines & Refrigerators: Is Impossible Possible?

    For the heat engine: First I converted all the temperatures to Kelvin, ηmax=1-(333)/(1000)=0.667 ηclaim=(1*10^3)/(1.75*10^3)=0.5714 So the heat engine seems to be less efficient than a Carnot heat engine which means it can exist. For the refrigerator: COPmax=(253)/(363-253)=2.3...
  7. QuasarBoy543298

    The second law of thermodynamics -- What does "from cold to hot" mean?

    in Clausius formulation, what does the phrase "from cold to hot" means? I can understand it intuitively but in the language of the zero and first laws, we have not defined a temperature scale, only equivalence classes of systems that will be in equilibrium with each other (systems with the same...
  8. E

    Why does the entropy of the Universe always increase?

    i don't really understand why S of the universe must be always positive,i know that only reversible process have constant entropy but why real proceses always increase S in the universe? sorry for bad english I am not from USA or UK
  9. F

    Machine in Clausius' 2nd law of thermodynamics?

    Hi all, sorry for the condensed title of my post. Any other version of the question I'm trying to ask turned out to be longer than allowed. So, my question is about the wording in some versions of Clausius' statement of the 2nd law of thermodynamics. From time to time I read something like...
  10. T

    Entropy in the Brazil Nut Sorting Effect

    In Brazil Nut effect /Granular convection the large grains move upward and the smaller ones go downward. This sorting is supposed to reduce the multiplicity of this system. But according to the second law of thermodynamics, entropy and multiplicity of the system should increase. I am looking...
  11. R

    I Heat death of the universe and the 3rd law of thermodynamics

    If the universe keeps expanding and eventually ends in a "big freeze" or heat death, does this contradict the third law of thermodynamics? The third law of thermodynamics states that a crystal at absolute zero has zero entropy. Since the entropy of the universe can never decrease, as the age...
  12. D

    Van der Waal expansion and delivered work

    Homework Statement Assume that one mole of an ideal van der Waals fluid is expanded isothermally, at temperature T_h from an initial volume V_i to a final volume V_f. A thermal reselvoir at temperature T_c is available. Apply dW_{RWS} = \left ( 1 - \frac{T_{RHS}}{T} \right ) (-dQ) +(-dW) to a...
  13. shihab-kol

    Does Building Construction Defy the Second Law of Thermodynamics?

    From what I know, the law says that disorder increases over time. But, when a building is constructed the disordered bricks,cement etc. take form of the ordered building. Am I wrong or is this an exception?
  14. M

    Doubts Arising from Clausius' Inequality and the Second Law

    I began reading Mehran Kardar's Statistical Physics of Particles and about halfway through the first chapter, there was a discussion on the second law of thermodynamics. He makes no mention of the old tenet that 'the total entropy in the universe must always increase' (I'll refer to this as the...
  15. Nemo's

    Determine the coefficient of performance of this cycle

    Homework Statement In an ideal refrigeration cycle, the temperature of the condensing vapour is 40oC and the temperature during evaporation is -20oC. Determine the coefficient of performance of this cycle for the working fluids; R12 and ammonia. Homework Equations C.O.Pc = TL/(TH-TL) The...
  16. V

    Doubt from second law of thermodynamics

    qrev/T = ΔS here what does ΔS signify?does it mean change in entropy of system or surroundings? how is entropy of system,surrounding and universe related to each other and which entropy is used in gibbs free energy equation?
  17. weezy

    I Doubt regarding proof of Clausius Inequality.

    I have attached two images from my textbook one of which is a diagram and the other a paragraph with which I am having problems. The last sentence mentions that due to violation of 2nd law we cannot convert all the heat to work in this thermodynamic cycle. However what is preventing the carnot...
  18. Z

    Thermodynamics: Irreversible process and entropy

    Homework Statement Hi ! I'm stuck with these two questions of my assignment of thermodynamics - Give two exemples of irreversible process (initial state, process, final state) - For each of them, explain why they are irreversible on the microscopic scale. Homework Equations We are not asked...
  19. O

    Using a hot gas to drive a piston: entropy reduction?

    Suppose we have an insulated cylindrical container with a piston inserted from one end. Suppose the volume confined by the piston is full of a hot gas. Now let the gas drive the piston so that the volume is increased. Did the entropy of the system decrease because some of the energy of the...
  20. kyle Bacon

    Does the atmosphere cool with altitude due to gravity?

    I read an article a day or so ago titled Hydrostatic Lapse, which makes the case for a phenomenon that I thought was well and truly confirmed; that gravity is responsible for the cooling of air with altitude. However I discover in the sequel article The Gemini Cycle that this phenomenon is...
  21. Robsta

    Entropy change of a reservoir after heating something up

    Homework Statement 1kg of silver is heated by a large heat reservoir at 373 K from 273K. Calculate the change of entropy in: a) the silver b) the reservoir c) the universe. Homework Equations ΔS = ∫dQ/T The Attempt at a Solution calculating the change in the silver first ΔS = ∫dQ/T...
  22. R

    Adiabatic irreversible expansion

    This example is taken from the wikipedia page describing irreversible processes. I just want to make sure I understand correctly why the initial state can't be reached anymore. I assume the transitions to be quasi-static, but there is friction between the piston and the cylinder. If so...
  23. 2

    Confused about the Carnot engine?

    I am teaching myself thermodynamics (and really enjoying it!) but am slightly confused about Carnot's engine. From the equation efficiency=1-T(cold reservoir)/T(hot reservoir), I see that the most efficient engine is one where the difference in temperature between the cold and hot reservoirs is...
  24. Filip Kierzek

    Probabilistic particle-scale valve with no moving parts

    Hi, Smoluchowski's trap door was proven to fail to obtaining work in a system without heat difference. The problem turns is random movement of trap door due to random particle movements. However I could not find any discussions of such system where the "trap door" did not involve moving parts...
  25. CaptCoonoor

    Universe : Can time move backward (New theory special)

    So, Hey Guys, I was watching DNews and Suddenly I came across this video. Also I found two sources of 'theory' Source A ; Source B; Seems like they are saying Entropy isn't the factor Explaining time, They even said that Thermodynamics (and it's second law) isn't what explains the time, They...