Irreversible Definition and 128 Threads

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

hi all, this is Entropy Rate Balance for Control Volumes. in the case of throttling process, .throttling process is irreversible process, so (S2- S1) must be greater than zero. what i want to know is to prove that (s2-s1) is greater than zero. Thank you in advance.

Homework Statement In an adiabatic irreversible expansion of ideal gas , if Pext = 0 then which is true, A. T2=T1 B. Q=0, C. P1V1= P2V2 D. P1V1γ= P2V2γ Homework Equations ΔU = Q - W For ideal gas, PV= nRT[/B] ΔU ∝ ΔT The Attempt at a Solution I know Q= 0, Work done is zero, So ΔU = 0, hence...

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...

The equation for entropy S=delta(Q)/T is derived from reversible processes such as Carnot cycle. The delta(Q) in the equation is the reversible heat added or taken out from the system. So, why is this equation valid in the case of processes like cooling of a body which is irreversible?

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...

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...

I was studying 2nd law thermodynamics. In that context found the clausius's inequality saying closed integral of dQ/T <0 for irreversible process. And from the reversible process entropy was defined. And from that view they said that for irreversible process dS>dQ/T. Now when I saw some...

Hi there, I was wondering if you could help me, I think I may have some concepts wrong or incomplete. Homework Statement We have an adiabatic cylinder of volume ##V_1## filled with a gas of pressure ##p_1## and temperature ##T_1## in thermal equilibrium, closed with a piston. All of a suden...

I was able to derive the work done in a reversible isothermal expansion. There as the P changes to P-dP, the volume increases by dV and hence the internal pressure also decreases by dP and equilibrium is maintained. (Thanks to @Nugatory and @Chestermiller fo r explaining it). Now when we take an...

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...

I know that gibbs free energy for say a body will be equal to = Gibbs free standard energy at 1M and Ph7(-rtlnkeq) (Where k is the concentration of product/ concentration of reactant at equilibrium)+rtlnk. How can we use the standard gibbs free for irreversible spontaneous processes? Is it...

I am studying Reif's Fundamental of Statistical and Thermal Physics. (p.91) he explain about Reversible and Irreversible processes by using "The number of accessible states in equilibrium(Ω)". in his point of view, each accessible states have equal probability. comparing to weather...

Homework Statement I know that the equation ΔSsystem = Q/T is only valid for a reversible process but whenever i see problems involving a irreversible isothermal expansion of ideal gas, the ΔSsurroundings is taken as -Qirr/T. Why is that equation valid for surroundings, is it because the...

Hello, It is said that any process accompanied by dissipating effects is an irreversible process.For instance, a piston cylinder arrangement undergoing an expansion of a gas with heat lost as friction between surfaces is an irreversible process.Here the system does work on the...

Why are precipitation reactions are irreversible as NaCl + AgNO3 --------> AgCl + NaNO3

I was following along in my Thermodynamic textbook and began playing with some definitions. In the following formulation, I somehow managed to prove (obviously incorrectly) that dq = TdS for even irreversible processes. I was hoping someone could point out where in the proof I'm going wrong...

Imagine a rigid block of steel at 100 degrees celsius which is inserted into water at 0 degrees celsius. They then both get an equilibrium temperature. How can I tell whether this is a reversible or irreversible process? What is the argumentation?

Hi 1) I am reading Pippard's Classical Thermodynamics and was confused by one of his examples in the attachment. What I do not understand is the concept of using P' (I am thinking P' as = P_fric + P_interface) for work calculations. If I take the system as composed of just the gas inside...

Why are precipitate and gas evolution reactions irreversible ( why don't the products react once again ) ??

One mole of an ideal monatomic gas initially at 298 k expands from 1.0 L to 10.0 L. Assume the expansion is irreversible, adiabatic, and no work is done. Calculate delta S of the gas and delta S of the surroundings. I know that delta dS = dq/T but q = 0 in adiabatic processes right? So does dS...

Hello everyone, I've been reviewing some concepts on Thermodynamics and, even though I feel like I am gaining a level of comprehension about the subject that I could not have achieved before as an undergraduate, I am also running into some situations in which some thermodynamic concepts seem to...

Homework Statement So I came down with something and missed some class and am making it up from others notes which arent entirely clear plus the long weekend for turkey day and I am really hoping someone can help me make some sense of this... I am trying to come up with the derivations for...

There are 2 types of reactions 1) Being fully irreversible and 2) reversible So for 1) the graph of Gibbs energy against the progress of reaction would look like this: http://postimg.org/image/phycri0vr/ So the difference between 100% product and 100% reactant is the ΔG of the reaction...

Homework Statement Suppose 100g of ethane (C2H6) expands isothermally at 350C from 50ml to 2L. Calculate the heat and work done by the system and the change in entropy if: i)The process is via a reversible path. ii)The process is non-reversible. I don't know how to answer ii) Homework...

For an irreversible process: S2 - S1 > ∫12 dQ/T In the case of heat transfer dQ between object with T1 to object with T2, T1 > T2 ΔS in Joules/K is known But for evaluating ∫12 dQ/T = ln dQ/T - ln dQ/T . d/Q is known but what values for T in this case ? Object 1 & 2 have Temperatures before...

Homework Statement Consider the adiabatic expansion of .553mol of an ideal monatomic gas with CV,m = 3R/2. The initial state is described by P = 6.25bar and T = 306K. Calculate the final temperature if the same gas undergoes an adiabatic expansion against an external pressure of P = 1.25bar to...

Hi, I have read that for an irreversible process the equation for the entropy is: $$ds>\frac{dQ}{T}$$ But if I regard a cylinder connected to a heatreservoir and want to callculate the entropychange of this cylinder, why can I use the equation: $$ds=\frac{dQ}{T}$$? THX

Hi, I am thinking about the Carnot-Cycle-Process. I know that a heat exchange is always irreversible. But in the Carnot-Cycle, there is heating too. Why is that kind of heating, in the Carnot-Process reversible? Thx Abby

Hi, I regard a irreversible cycle process. It is a cylinder filled with gas, which underlies the following processes: 12: isothermal compression (reversible) 23: adiabatic expansion (reversible) 31: isochor heating (irreversible) [This happens by connecting the cylinder with a...

Two questions: 1. What does the T-s diagram look like for the irreversible cycle? 2. Do the isentropic efficiency equations that you apply to turbines and compressors (especially in the Rankine cycle) apply to the theoretical "turbines" and "pumps" in the Carnot cycle?

Stirling engine: the cycle is composed by two isothermals and 2 isometrica and there are just two heat reservoirs. By the isometrics I would say that that it is irreversible since you exchanging heat with a reservoir at a different temperature than your gas. However my notes say the...

Hi everyone, and happy new year if you happen to be reading this tomorrow. Rather than partying, I am writing up 100+ pages of astrophysics lecture notes, which I think will take infinite time as I keep getting stuck on every other line. My current problem is with the equation for the...

For reversible, work done =∫P dV Then for irreversible ,we can't use the above equation, because we have to consider the dissipative work. Correct? Thank you

Say I have a gas enclosed in a bottle with a weight on top exerting pressure P0. Let the gas pressure be P. If P0 is not equal to P the compression/expansion will be irreversible. If P0>P and the gas is being compressed: Work done on the gas is: -PdV Work done on surroundings by the gas...

According to my textbook, during an irreversible process, the entropy change of the surroundings is given by \frac{q}{T} where q is the heat transferred to the surroundings during the process. Why are we allowed to use this equation, considering that this equation only holds for reversible...

Homework Statement Show that processes involving rapid chemical reactions are irreversible by considering the combustion of a natural gas (e.g. methane) and air mixture in a rigid container. Homework Equations Q_{in}+W_{e,in}-W_{b}=\Delta U+\Delta KE+ \Delta PE The Attempt at a Solution I...

We learned about calculating entropy in my physics 2 class, and i came up with an example that my professor couldn't answer, so I was hoping someone here could shed some light on this for me. We learned that change in entropy for an irreversible process be represented by changes in entropy of...

Hello everyone. I have found quite a lot of conflicting information about the first law applied to irreversible processes and in particular whether the dS term in the equation dU = TdS - pdV only accounts for the entropy transferred or for the total entropy, i.e. dS_transferred + dS_created...

Entropy related questions -- Reversible or Irreversible? Homework Statement A 15.0kg block of ice at 0C melts to liquid water at 0C inside a large room that has a temperature of 20C. Treat the ice and the room as an isolated system, assume that the room is large enough for its temperature...

Trying hard to understand a basic textbook model meant to illustrate that entropy (of the universe) increases for irreversible processes. Help me out please? I get this part: A gas is compressed isothermally (constant T) and reversibly, getting worked on and expelling heat. To calculate ΔS...

Homework Statement I know how to do the problem so I don't need help actually solving it, I just don't understand the concepts. A sample of 4.5g of methane occupies 12.7L at 310k. a) Calculate the work done when the gas expands isothermally against a constant external pressure of 7.7 kPa...

When a hot stone is dropped into a lake the change in temperature of the lake is negligible, but the stone cools down and so its entropy decreases. Is this therefore a case of an irreversible process in which total entropy decreases? This isn't for homework but for revision towards my resit. I...

From what I've read all processes of a thermodynamic system are irreversible because some energy will be lost to the surroundings but I don't understand why that can't be reversed by getting the surroundings to put that energy back into the system. Let's say I have a gas canister with a piston...

I don't seem to understand Clausius inequality at all. Really. It was deduced to me that the Clausius inequality is given by dS = \frac{\delta Q_i}{T} > 0 where Q_i is the irreversible heat transferred to a system. Though I cannot find a way to prove an assertion my teacher said: through...

Homework Statement I'm reading a book on Thermodynamic processes, and they argue that for an irreversible change dW\geq-PdV and I can't explain to myself why is this. Can anyone help?

1. A sample of methane of mass 4.5 g occupies 12.7 L at 310 K. Assume that the gas behaves ideally. (a) Calculate the work done when the gas expands isothermally against a constant external pressure of 30.0 kPa until its volume has increased by 3.3 L. (b) Calculate the work that would be done...

i can't seem to get something in classical thermodynamics entropy is a state function of a system,that means it only depends on the state of a system not time or path. if i have an irreversible process between state 1 and state 2, and back to state 1, and i want to know the entropy change of...

What is the concept behind 'irreversible adiabatic process' ? Why is the expression for work done in this case different from that when it is reversible?

I need some clarification on the following points on the reversible and irreversible reactions. In the examples cited in textbooks, for reversible reaction, isothermal expansion and compression are given. But the adiabatic exp and comp are not given. Why is it not included in the list...