What is Reversible: Definition and 247 Discussions

Reversible computing is a model of computation where the computational process to some extent is time-reversible. In a model of computation that uses deterministic transitions from one state of the abstract machine to another, a necessary condition for reversibility is that the relation of the mapping from states to their successors must be one-to-one. Reversible computing is a form of unconventional computing.
Due to the unitarity of quantum mechanics, quantum circuits are usually reversible.

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  1. L

    A simple question about reversible heat

    Is it possible to heat a specific amount of liquid water, say 1kg, (at 1 atm), let's say from 20°C to 21°C, without changing the universe's entropy? (Sorry but I have a little blackout on simple thermodynamics...) -- lightarrow
  2. Ryaners

    Thermo: isothermal, reversible expansion of ideal gas

    Homework Statement Two moles of a monatomic ideal gas are at a temperature of 300K. The gas expands reversibly and isothermally to twice its original volume. Calculate the work done by the gas, the heat supplied and the change in internal energy. So: T = 300K; ΔT = 0 n = 2; R = 8.314 J K-1...
  3. Ali Abbas

    B Black Holes & Reversible Time: Exploring Possibilities

    When somebody crosses the horizon of a black hole, the person would have the privilege to travel backwards in time (as shown in the movie 'Interstellar'). What are the possiblities of such a person to even survive after getting in a black hole, and how does he even able to travel in the past...
  4. R

    Heat Engine problem in Thermophysics

    Homework Statement Im working on the following problem and could need some help in answering them: Work is being produced from a cycle. In order to produce this work, energy is being taking from a high temperature sources at a ratio of 1000 kJ/kg and the extra energy is being deliver to a...
  5. S

    Energy change of reservoir in reversible weight process

    In what follows I refer to the ideas of "Thermodynamic: Foundations and Applications" by Gyftoploulos and Beretta. The abbreviated form of my question is: In a reversible weight process, Ω1R-Ω2R = E1 - E2 (see eqn. 6.18, p. 99) is transferred out of the composite of a system A and a reservoir R...
  6. T

    Carnot Cycle with negative temperatures

    Homework Statement Heat engines at negative temperatures. Consider using two heat reservoirs to run an engine (analogous to the Carnot cycle of chapter 3), but specify that both temperatures, T_hot and T_cold, are negative temperatures. The engine is to run reversibly. (a) If the engine is to...
  7. TheExibo

    Why do reversible reactions occur in the first place?

    It is generally said that reactants react so that they can achieve a lower energy state. Then why does a reversible reaction occur in the first place? If catalysts lower activation energy both ways in a reversible reactions by making the transition state less thermodynamically unfavourable...
  8. E

    Entropy Change in a Reversible Process multiple phase change

    Homework Statement (a)How much heat must be added to a block of 0.120kg of frozen ammonia initially at 100oC to convert it to a gas at 80oC given the following information? (b) assuming this could be done using a reversible process what would be the total entropy change associated with this...
  9. mukul

    A Big debate: following process is reversible or not

    There had been a big time debate in my college between chemistry faculties and physics faculties on whether the following process is reversible or not. consider that there is some gas (assuming ideal gas) in a chamber with friction less piston of 5kg and 2 kg mass on top of it as shown in the...
  10. S

    Does efficiency always depend on reversibility of the engine?

    I'm confused on the efficiency of a Thermal engine in the case it is reversible or not reversible, in particular where the ideal gas follows isochoric or isobaric processes. Infact during isochoric and isobaric processes $$Q_{isochoric}=n c_v \Delta T$$ $$Q_{isobaric}=n c_p \Delta T$$ So the...
  11. S

    Reversible heat exchange between water and ice

    Homework Statement In an adiabatic container are placed , in rapid succession , a mass of ice , ##m_I= 2 kg## , at temperature ##T_I = -10 ◦C## and a mass of water , ##m_W = 1 kg## , at the temperature ##T_W = + 20 ◦C## . Determine : a) the total mass of water present in the container at...
  12. C

    Entropy change of environment during an irreversible process

    What is the change in entropy of thermodynamic environment if it changes its temperature during the process and the process is not reversible? I'm slightly confused because, on the one side, in that case ##\Delta S_{gas} \neq -\Delta S_{surroundings}##, since ##\Delta S_{universe} >0## but on...
  13. Oribis

    Can Gas Expansion Be Reversed?

    Homework Statement Hello, new here! I have a question regarding reversible or irreversible expansions in regards to figuring which equation is needed to figure out work, W. For starters, here is the question: One mole of an ideal monatomic gas is expanded from an initial state of 3 atm and 500...
  14. M

    Quasi-static and reversible processes in thermodynamics

    Too much confusion in my head about these concepts... Is every reversible process quasi static? If not, what are some examples? If process is irreversible then it doesn't need to be non quasi-static, I understand that. (eg. free expansion of the gas) Can irreversible process be quasi static...
  15. S

    Question about Reversible Engines and Carnot Efficiency

    Homework Statement I have a question regarding heat engines that cropped up whilst I was doing a practice question. I will summarise the results I obtained for the previous parts of the question so as to save your time. The highlighted parts of the image are where I am having some issues. I...
  16. S

    Is Dropping a Metal Block into a Lake a Reversible Process in Thermodynamics?

    Hello all. I have a quick question about entropy... I've just been formally introduced to it. Consider the example of a metal block of mass m and heat capacity Cp at temperature T1 = 60C being dropped into a large lake of temperature T2 = 10C. $$\Delta S_{block} =...
  17. H

    Reversible endothermic reaction

    hi, In the past there were "toys" containing a fluid and a clip. When pressing the clip, the fluid became hard and it gave warmth. When the toy was boiled in water, it became fluid again and one could start over. Now I was wondering of there is a chemical reaction that gives cold instead of...
  18. S

    Entropy change in a reversible isothermal process

    Why does ∆S = 0 for a reversible process, but for a reversible isothermal process, ∆S is given by nRln(Vf/Vi) (or other variations of that equation)?
  19. A

    Reversible vs irreversible work for adiabatic process

    I have a gas transitioning adiabatically between A (P1, V1) and B (P2, V2) where P1>P2 and V2>V1. The question is to determine the net work done on the gas if the gas is first expanded reversibly from A to B (w = dE = Cv(T2-T1)), and then compressed irreversibly from B to A (w = -Pext(V1-V2)) at...
  20. entropy1

    Why is entropy not reversible?

    Is there an easy way to explain in layman terms why entropy in an open system is not reversible?
  21. W

    Finding work of adiabatic compressor using ideal gas

    Homework Statement Methane at ## P_1 ## and ## T_1 ## is compressed to a pressure of ## P_2 ## adiabatically at steady-state. Calculate the work done on the compressor and the temperature ## T_2 ## of the discharge gas. Use ideal gas model. Given: ## T_1, P_1, P_2, C_p, \gamma = 1.4 ## ##...
  22. A

    Calculating Reversible Work and Irreversibility in a Filling Container

    Homework Statement A rigid and evacuated container of volume V that is surrounded by atmosphere (P0, T0). At some point neck valve opens and atmospheric air gradually fills the container. The wall of container is thin enough so that eventually the trapped air and atm reach thermal equilibrium...
  23. A

    Reversible Work and Irreversibility

    I am trying to grasp the concepts of reversible work, irreversible work and irreversibility.(Last one is the difference between them if i am not mistaken.) Let us consider a rigid and evacuated container at volume V. Then, a valve opens and athmospheric air (P0, T0 is filling the tank. The wall...
  24. C

    Basic thermodynamics, reversible engine process

    Homework Statement http://i.imgur.com/jmLqca9.jpg pic of question Homework Equations W = p x dV, Q = dU + W etc The Attempt at a Solution I know what the different stages are, a-b and c-d are isobaric, d-a and b-c are isochoric and I believe the answer to a, the net work done in one cycle...
  25. RJLiberator

    Proof: 3 Reversible evolutions -- Hermitian Conjugate

    Homework Statement Consider a qubit whihc undergoes a sequence of three reversible evolutions of 3 unitary matrices A, B, and C (in that order). Suppose that no matter what the initial state |v> of the qubit is before the three evolutions, it always comes back to the sam state |v> after the...
  26. L

    Why is the Definition of Entropy Restricted to a Reversible Process?

    Even though entropy is a state function and thus independent of path why is it that the definition of entropy is restricted to a reversible process? Eq 1: dS=dqrev/T First of all, is this for an open system, closed system or isolated system? The Clausius inequality deals with the exchange...
  27. H

    Question about reversible adiabatic expansion

    Hello guys, I have some troubles to understand a reversible adiabatic expansion. we have dq=0 and dw=-pdV and for a perfect gas dU= Cv*dT. I don't really understand why dU= Cv*dT since we have a variation of volume and it is established that dU= Cv*dT when we haven't any modification of the...
  28. A

    Thermodynamics Problem - Adiabatic Reversible Process....

    Homework Statement A specific type of ideal gas has a specific heat capacity at constant pressure (cp=cv+R) that is a function of temperature T, such that cp=0.5+876T, where cp has units of J/kg/K and T has units of K. The gas, which is initially at T1 = 294 K and P1 = 1x105 Pa, undergoes a...
  29. ajayguhan

    Is a Process with Infinite Time and Finite Gradient Reversible or Irreversible?

    if the time taken by a system to execute a process through a finite gradient is infinitely large, then the process is reversible or irreversible?
  30. A

    Calculating reversible adiabatic expansion

    I have some homework that I am just not able to figure out. There is a 2kg parcel of air at T1=32°C and p1= 0.8 atm This parcel of air expands until it is at T2=12°C Also, during the expansion 3.2 g of water will condense due to the dT (ΔvapH (water) = 40.65kJ mol-1 Also: Cv=0.718 kJ...
  31. S

    Entropy change for reversible and cyclic process

    Homework Statement An ideal diatomic gas is initially at temperature ##T## and volume ##V##. The gas is taken through three reversible processes in the following cycle: adiabatic expansion to the volume ##2V##, constant volume process to the temperature ##T##, isothermal compression to the...
  32. Soumalya

    COP of Reversible Refrigeration Cycles

    Considering two thermal energy reservoirs, one at a higher temperature of TH compared to the other at TL, if we operate a reversible refrigeration cycle between the reservoirs then its coefficient of performance is given by, COPR,rev=TL/TH-TL This is the basically the maximum COP a...
  33. DavideGenoa

    Reversible cycle approximated by Carnot cycles

    My textbook gives the definition of a reversible transformation as a transformation that can be inverted by effectuating only infinitesimal changes in the surroundings. I admit that I have no idea of what infinitesimal means in a rigourous mathematical language, therefore the definition is quite...
  34. DavideGenoa

    Thermal efficiency: reversible and irreversible machines

    In the proof of Clausius inequality ##\oint\frac{\delta Q}{T}<0## for an irreversible cycle, I always find the fact that the thermal efficiency of an irreversible machine is **stricly less** than the thermal efficiency of a reversible machine, both operating between temperatures ##T_H## and...
  35. Jimster41

    B Is Reversibility Real or Just a Mathematical Concept?

    is there any real instance of a reversible process or are such operations only possible mathematically, only in the abstract? I know this might seem like a dumb question, but I am confused by it.
  36. Chestermiller

    Reversible Vs Irreversible Gas Compression/Expansion Work - Comments

    Chestermiller submitted a new PF Insights post Reversible Vs Irreversible Gas Compression/Expansion Work Continue reading the Original PF Insights Post.
  37. N

    Reversible Carnot Cycle: Exploring Heat Dynamics & Conservation

    In a reversible carnot cycle the amount of heat added is always more than the amount of heat taken out. So why doesn't it explode? I'm wondering how heat is conserved mathematically as the area under the curve of a p-v diagram. u=q+w. If the heat during expansion is always more than the heat...
  38. S

    Adiabatic Free Expansion and Reversible Isothermal Path

    Homework Statement Consider an ideal monatomic gas that undergoes an adiabatic free expansion starting from equilibrium state A with volume 500 cm3, pressure 40 kPa and temperature 300K to state B, which has a final equilibrium volume of 1000 cm3. Construct an reversible isothermal path that...
  39. S

    What does the maximum work of a reversible expansion mean?

    What does it mean by maximum work of an isothermal, reversible expansion of a perfect gas from initial volume Vi to final volume Vf at temperature T? I understand that heat enters the system during this expansion to ensure that no internal energy is lost but it doesn't really help in anyway...
  40. P

    Thermodynamics. Irreversible and reversible Process

    When we were taught these in the class. There were a few terms I did not understand which my school teacher used. Firstly, they told us that the work in a reversible process occurs at the boundary of the system, an acceptable fact. All the energy is converted yo work done, and then showed us a...
  41. M

    Polish Physics Olympiad: Proving Adiabatic Reversible Process

    Homework Statement (56th Polish Olympiad in Physics, 2007) We have a tube of mass ##M##, consisting of two segments of diameters ##d_1, d_2##. The pistons (see the picture http://www.kgof.edu.pl/archiwum/56/of56-2-1-R.pdf) have mass ##m_1, m_2##. At the start the air inside had pressure...
  42. B

    Reversible and Irreversible Expansion

    What's the difference between reversible and irreversible expansion? I know how they are in formulas, (Irreversible-PV, reversible- integral over P in terms of V), but why are they expressed like this? What's the difference? And I would also like to get an exact formula of these two as I can't...
  43. I

    Calculating the End Temperature of Adiabatic Compression for an Ideal Gas

    Homework Statement Air is compressed at room temperature from atmospheric pressure to ##\frac{1}{15}## of the initial volume. Calculate the temperature at the end of compression assuming the process is reversible and adiabatic.Homework Equations ##pV^\gamma = constant \Longleftrightarrow T...
  44. L

    Reversible adiabatic expansion proof

    Homework Statement Prove the relationship between the pressure, P, and the temperature, T, for an ideal gas with a reversible adiabatic expansion. Base the proof on the first law of thermodynamics and the ideal gas law. The relationship is: T^(Cp,m/R)/P = constant Where R is the gas constant...
  45. E

    Work done by product gas in reversible adiabatic expansion

    I am having trouble calculating the work done by a product gas in reversible adiabatic expansion, and in calculating the final temperature. pV gamma = constant, Cv = constant (assume), gamma = cv + nR / Cv. anyone who can help me out?
  46. kelvin490

    Is Carnot engine the only reversible engine?

    Is Carnot engine the only form of reversible engine? Is it possible to have a different form of reversible engine that goes through different processes? For a standard Otto cycle working with ideal gas, theoretically the two processes involving isochoric pressure change can be reversible...
  47. A

    Irreversible vs Reversible process

    I know that to calculate the entropy change in a process, I just need to calculate the entropy change in a process that has the initial and final states of the process and is reversible. I just don't understand what the actual difference between the irreversible versus the reversible process is...
  48. M

    Maximum work can be obtained from reversible process ?

    My book says 'Maximum work can be obtained only from thermodynamically reversible processes,' but why is it so? What is the cause? Actually to me the definition of reversible process is confusing. It says that at each step during the process, equilibrium is maintained. But, let's say,we have to...
  49. Useful nucleus

    Is every reversible process coincident with a quasi-static process?

    For a closed system: If we define a quasi-static locus (process) as an ordered and dense succession of equilibrium states in the thermodynamic configuration space. Then we define a reversible process as one in which no entropy is generated. Then it is clear that there are some quasi-static loci...
  50. Chacabucogod

    Carnot Reversible Machine: Exploring the Impact on 2nd Law of Thermodynamics

    I was reading Cengel's thermodynamics and noticed that he uses a thought experiment to show that there is no machine that is more efficient than the Carnot reversible machine. He says that both a reversible machine and an irreversible machine are connected to high and low temperature deposits...
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