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. T

    Work done in a reversible adiabatic expansion

    Hi there! I have to determine the work done of a reversible adiabatic expansion. Becauce the system is adiabatic: Q = 0 so \DeltaU = Wrev Becauce both the pressure and the volume changes I can't use W = pex\DeltaV. Homework Statement Cv, Cp, Ti, Tf, Pi, Pf, Vi, Vf are known The Attempt...
  2. T

    Compare burning of fuel to reversible supply of heat

    Hi! I'm working on a problem regarding a jet engine and I actually did solve it but I'm not sure about two things: At some point in the engine, air is heated at constant pressure (with the gas being almost stationary). Of course, this is done by the burning of fuel. But I found the...
  3. G

    Reversible Process: Final Temp Calc of Argon Mass 12.0g

    Homework Statement Calculate the final temperature of a sample of argon of mass 12.0 g that is expanded reversibly and adiabatically from 1.0 L at 273.15 K to 3.0 L. Homework Equations The Attempt at a Solution n = 12[g]/40[g][mol]-1 = 0.3 [mol] pVi=nRTi p =...
  4. 1

    Reversible Heating and Cooling

    Homework Statement I have two problems. What is Delta U, Delta H, q, and w for the Reversible heating of an ideal gas at constant P. Also, what are these values for the Reversible cooling of an ideal gas at constant V. Homework Equations The Attempt at a Solution For the...
  5. D

    Reversible cycle and adiabatic expansion

    Homework Statement One mole of a monatomic ideal gas is taken through the reversible cycle shown below. Process bc is an adiabatic expansion, with Pb = 10.0 atm and Vb = 1.00 x 10-3 m3. Find (a) the energy added to the gas as heat (b) the energy leaving the gas as heat, (c) the net work done...
  6. W

    Isothermal reversible expansion

    Homework Statement Calculate the work done during the isothermal reversible expansion of a gas that satisfies the virial equation of state. Homework Equations Virial equation of state: pVm = RT(1+B/Vm + C/Vm + ...) Isothermal reversible expansion: w = -nRT ln(Vf/Vi) The Attempt at a...
  7. J

    Is time reversible in Quantum Math?

    In a "Briefer History of Time" Hawking says what everybody else does: that the laws of physics do not indicate a preference for time running forward or backward. He says that the forward direction may be required somehow by the increase of entropy from the highly ordered state of the...
  8. K

    Self-Adjoint Operators and Reversible Logic gates

    Does anyone know if there is a relationship between the requirement in Quantum Computing that logic gates be reversible and the requirement in Quantum Mechanics that observables have to be self-adjoint?
  9. A

    Reversible processes and carnot cycle

    i want to ask why heat transfer is considered ti be an irreversibility and why in carnot carnot cycle heat addititon is at constant temperature to make this process reversible
  10. C

    Entropy for reversible and irreversible cycles.

    I am confused about the entropy change for reversible and irreversible cycles. I know entropy is a state function, so for cycles, the entropy change within the system should be 0, since the process ends up in the same state as the beginning. So does this mean that the entropy change for the...
  11. C

    Thermal efficiency in a reversible cycle for an ideal gas pV diagram

    Homework Statement A heat engine takes 4.0 moles of an ideal gas through the reversible cycle abca, on the pV diagram, as shown. The path bc is an isothermal process. The temperature at c is 600 K and the volumes at a and c are 0.04 m^3 and 0.10m^3, respectively. The molar heat capacity at...
  12. K

    Reversible, equilibrium and quasi-static

    Hi there, I found it is too much concepts in my head after reading more and more about thermodynamics. In the very beginning of the text, it emphize that in many cases (at lease in beginning level), we only deal with the equilibrium state in thermodynamic system. To make sure every stage of...
  13. K

    Entropy Changes in Reversible Engines: Is the Total Change Always Zero?

    I learned Thermodynamics long time ago, forgot most of the content. I just want to ask I question. For a reversible engine, no matter how many complete cycles it done, the total change of entropy of the engine will always be ZERO, right? What about the change of entropy of the universe in...
  14. H

    The principle of reversible Kater's pendulum and why its rod's ends are pointed

    I am not able think of convincing answers to the following questions- 1.Why the distance between knife edges (when the time periods about them is approx same) is considered equal to the length of an equivalent simple pendulum ?? It will be great if you can derive it... 2. Why the ends of the...
  15. I

    Need help understanding sceanario only, is it a closed reversible system?

    Homework Statement @= alpha= thermal expansion coefficent= 5.1x10^-5 Kt= compression= 3.2x10^-5 B=beta= -(dE/dV)t = 0.5 Po=1 atm To=293K Vo=1L ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Solid held in a piston and cylinder at equilibrium is in a constant temperature bath at 293k. Two...
  16. S

    Reversible Composite Heat Engine 3 Reservoirs

    Homework Statement A reversible composite heat engine operates between three reservoirs at temperatures of 400K, 300K and 200K. One engine operates between the 400K and 300K reservoirs and a second engine operates between the 300K and 200K reservoirs and is synchronised with the first. In...
  17. A

    Maximum work during reversible process?

    maximum work during reversible process? I have seen maximum work is achievable when the process is carried out reversibly. Is it correct? For example, if you look at the following problems, 1) Ten litres of an ideal gas at a pressure of 10 atm expands isothermally against a constant...
  18. C

    Equation for work of a reversible isothermal compression

    I need to find the equation for the work of a reversible isothermal compression of 1 mol of a gas in a piston/cylinder assembly if the molar volume of the gas is given by V= ((RT)/P) + b where b and R are positive constants. Not sure what to do .. please help! THANKS
  19. M

    Thermo reversible heat engines physics question

    I am having trouble with this question...It is from "applied thermodynamics for engineering technologists" by Eastop (Q5.2 if anyone has it)... The Question: Two reversible heat engines operate in series between a source at 527°C and a sink at 17°C. If the engines have equal efficiencies and...
  20. M

    Reversible expansion according to a law pv^2 = constant

    A fluid at 0.7bar occupying 0.009m3 is compressed reversibly to a pressure of 3.5bar according to a law pv^n = constant. The fluid is then heated reversibly at constant volume until the pressure is 4bar; the specific volume is then 0.5m3/kg . A reversible expansion according to a law pv^2 =...
  21. S

    Equation apply to reversible only or not?

    Equation apply to reversible only or not?? My thinking must be faulty somewhere, but I can't work out what's gonig on... The equation Tds = du + pdv and du = dq + dw are supposed to be valid for all processes right? yet dw = -pdv only for reversible cases, yes? So how do you...
  22. A

    Reversible adiabatic expansion/compression equal to zero

    So, I am looking a question about adiabatic expansions and the associated entropy changed. Why exactly is the change in entropy for a reversible adiabatic expansion/compression equal to zero? The book says its because there is no heat transfer, but for irreversible adiabatic processes, there...
  23. C

    Is a reversible isothermal process truly without energy change?

    Hi! I was just wondering if in a reversible isothermal process, there is a change in internal energy. I know that for the isothermal forward process the temperature is constant so internal energy is constant? What really stumps me is the word reversible.
  24. A

    Is every mechanical process or mechanical reversible?

    Is evry mechanical process or mechanism reversiible? By that i mean to say, Can we carry out every mechanism or process in reverse? for eg: if i have a mechanism which converts rotary motion to oscillatory, can i use the same mechanism for changing the oscillatory motion to rotary, without...
  25. E

    Thermodynamics, isentropic and reversible processes

    Hi, I have some questions regarding thermo: 1) Does an isentropic process have to be a quasistatic one? What is the relation between equilibrium and reversibilty? 2) Naturally, there are revesible processes involving control volumes. A gas can go through an isentropic process in a reversible...
  26. A

    How Much Work Can a Reversible Heat Engine Generate?

    [/B]Homework Statement What is the maximum amount of mechanical work that can be got by a reversible engine working from a finite heat source of thermal capacity, C=1000J/K, if it is initially at 373K and the engine discharges to a bath of virtually infinite heat capacity at 273K? [You may...
  27. L

    Isothermal and reversible expansion work problem (Physical Chem)

    Homework Statement A sample of 2.00 mol. CH3OH (g) is condensed isothermally and reversibly to liquid at 64*C. The standard enthalpy of condensation of methanol @ 64*C is -35.3 kJ/mol. Find w and q for the reaction. Homework Equations w = -nRT * ln(Vf/Vi) (although I don't have volume...
  28. C

    How can we determine if a reaction is reversible or not?

    how can we determine if a reaction is reversible or not? Zn2+ (aq) + 2e- -> Zn(s) is this a reversible reaction? thanks! :biggrin:
  29. D

    Reversible process of heated pot

    Homework Statement A pot is half filled with water and concealed by a lid so that no vapor can escape. The pot is then heated on a stove so steam is formed inside the pot. Now the heat is turned off and the vapor condenses into water. Explain when the process is reversible/irreversible. The...
  30. A

    Reversible and irreversible process?

    please explain me in easy words . what is reversible and irreversibe process and give some daily examples. thank you.
  31. B

    Reversible Thermo-Chemical Reactions

    Does anyone know where I can find information on these kinds of reactions such as the possible chemical combinations, reactions and decomposition temperatures, energy stored and released per unit mass, etc? Thanks! -Brendan
  32. A

    Thermodynamics: reversible process, equilibrium and entropy

    Hi, everyone. i have several questions about thermodynamics which I just read. 1. Why does a reversible process require equilibrium of the system all the time? 2. Is every process reversible if it's very very slow so that the system is in equilibrium all the time( and there's no friction...
  33. S

    Conditions are adiabatic and reversible about a turbine

    Why is it when the conditions are adiabatic and reversible about a turbine, the assumption is its isentropic?
  34. K

    How Do You Calculate Entropy Change in a Reversible Cyclic Process?

    An ideal gas undergoes a reversible, cycli process. First it expands isothermally from state A to state B. It is then compressed adiabatically to state C. Finally, it is cooled at constant volume to its original state, A. I have to calculate the change in entropy of the gas in each one of the...
  35. DaveC426913

    Reversible Ceiling Fan: Benefits & Functionality

    (I think I've actually asked this before...):blushing: I have a standard 3 speed reversbile ceiling fan. The reverse switch of course changes it from blowing air up to blowing air down. What is the benefit of reversing the fan? Most people seem to think that it constitutes a difference...
  36. J

    Cyclic Machine: Reversible Process?

    A cyclic machine receives 325 kJ from a 1000 K energy reservoir. It rejects 125 kJ to a 400 K energy reservoir, the cycle produces 200 kJ of work as output. Is this cycle reversible, irrerversible, or impossible? Not exactly sure what he is looking for here. But, since W=QH-QL, does that mean...
  37. P

    Incomplete/ Reversible reaction

    I didn't catch yet the difference between an incomplete and a reversible reaction. I think they are the same. Or there is any reaction that is incomplete but not reversible? Or one that is reversible but not incomplete?
  38. S

    Find Heat, Work & Internal Energy for Reversible Expansion of Gas

    we have an ideal monatomic gas which intially occupies 27*(10^-3) m^3 at a pressure of 3.2*(10^5) Pa and at a temperature of 400K. We have to find the heat supplied to the gas, the work done on it, and its increase in internal energy when it is compressed isothermally at 400K to a volume of...
  39. K

    Change in entropy in irreversible and reversible process

    It is stated that the change in entropy of an isolated system during an irreversible process is > 0; while for a reversible process, it is = 0. An isochoric process has a change in entropy given by : nCv(Pf/Pi). Does this mean that it is an irreversible process? ARen't isochoric processes...
  40. A

    Efficiency and Performance of a Reversible Heat Engine

    for the following question: a reversible heat engine, opearting in a cycle, withdraws heat from a high-temperature reservoir(the temperature of which consequentyly decreases), performs work w, and rejects heat into a low-temperature reservoir(the tempertaure of which consequentyly increases)...
  41. DaveC426913

    Physics of a reversible ceiling fan

    I often hear people suggest switching the direction of a ceiling fan from 'blow' to 'suck' or the reverse, thinking that one will draw cool air in better. My intuition tells me that: - a ceiling fan blows air in a doughnut patterrn, where air flows either up in the centre or down in the...
  42. Q_Goest

    Reversible Computation: Feasible?

    This regards an article found in the journal of Nature, 26 Aug. '04. I thought it might be interesting, not so much for the physics it presents (although they are certainly fascinating) but because of the implications. I think a discussion around the questions provided at the end of this essay...
  43. Y

    Quasistatic processes are reversible?

    It's probably a silly question. I know definitions of quasistatic and reversible process. How can we proove that each quasistatic process is reversible? Before it went for me without saying. But now I noticed that I can't proove it. In books that I have this conclusion is made after both...
  44. H

    Calculating Cost of 1KWhr Heat from a Reversible Heat Pump

    A perfectly reversible heat pump heats a building at 20deg from the atmosphere at 5deg. If the heat pump is run by an electrical motor whose efficiency is 80%, what is the cost of 1KWhr of heat supplied? (1KWhr of electricity is 6p) I am confused by this qn as I thought the efficiency, e =...
  45. W

    Reversible heat exchange with surroundings

    why is it acceptable to assume any heat exchanged with the surroundings of a system is a reversible heat exchange? The only explanation I can find is that it's because the surroundings are essentially unchanged by the heat they absorb...but I don't understand that as an explanation. I take...
  46. L

    Is radioactivity decay reversible or irreversible?

    is radioactivity decay reversible or irreversible?
  47. A

    Work done in a reversible adiabatic change

    Can anyone help me with this? -- Show that the work done in a reversible adiabatic change from an initial state (p1, V1) to a final state (p2, V2) is: W = ( p2V2 - p1V1) / (gamma - 1) -- Here's what (little) I have done so far: Reversible => dW = -pdV Adiabatic => dq = 0...
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