(a) What is meant by calling a process irreversible? (b)...

Name: Problem 18, Chapter 19: Chemistry The Central Science
Uploaded: 2021-06-23T00:31:17-08:00
Duration: 4 min 32 s
Channel: Christopher Nilsen
Description: (a) What is meant by calling a process irreversible? (b) After a particular irreversible process, the system is restored to its original state. What can be said about the condition of the surroundings after the system is restored to its original state? (c) Under what conditions will the condensation of a liquid be an irreversible process?

(a) What is meant by calling a process irreversible? (b) After a particular irreversible process, the system is restored to its original state. What can be said about the condition of the surroundings after the system is restored to its original state? (c) Under what conditions will the condensation of a liquid be an irreversible process?

Key Concepts

Non-equilibrium Phase Transition (Condensation Conditions)

The process of condensation is reversible only under conditions where the system remains nearly at equilibrium, meaning the temperature gradients driving the phase change are infinitesimally small. In practical scenarios where condensation occurs with finite driving forces or temperature differences—resulting in rapid or non-quasi-static transitions—the process becomes irreversible due to the production of entropy and the dissipative effects associated with the sudden phase change.

System and Surroundings in Cyclic Processes

When a system undergoes an irreversible process and is later restored to its original state, the surroundings typically do not return to their original condition. This is because irreversible processes generate entropy and require that some energy (or heat) is irreversibly dissipated into the environment, leaving a permanent change in the surroundings even though the state of the system appears unchanged.

Irreversible Process

An irreversible process is one in which the change cannot be undone by an infinitesimally small modification in conditions. These processes inherently involve phenomena like finite gradients, friction, or dissipation, which lead to the production of entropy. This means that even if the system is restored to its original state, the process cannot be retraced exactly without additional changes to the surroundings or environment.

Reversible Process Contrast

A reversible process is an idealized change that occurs so slowly and under infinitesimal gradients that the system remains in thermodynamic equilibrium at all times. In such a process, both the system and its surroundings can be returned to their initial states without leaving any net change in the universe, which contrasts with the intrinsic entropy production of an irreversible process.

Transcript

00:01 So let's talk about the differences between a reversible and an irreversible process.

00:05 In a reversible process, if we make very small changes from one state to another and back, we will not have affected the overall entropy of the universe.

00:20 However, in an irreversible process, we can go from state one, wherever we start, to state two, and we can wind up going backwards, and we can actually get back to state one.

00:45 We can get back to the initial conditions of the system.

00:49 So infinitesimal changes will, or i guess i could say could, bring the system back to the original state.

01:15 But remember that the universe is made up of two places.

01:20 It's made up of the system and the surroundings.

01:26 And so we have the second law of thermodynamics that says that the entropy of the universe is always increasing.

01:35 And so when we have the change in entropy of the universe as being the change of the system and that of the surroundings, we might be able to get the system back to where it was originally by these infinitesimal changes back and forth, but what we know is that the entropy of the universe is always increasing, which means that in an irreversible process, even if we get back to the system's original state, the surroundings will have its entropy increased.

02:11 Now, there are some places, some things in nature that you could see if we have a particular temperature and pressure condition where we will have a reversible process.

02:32 For instance, if we boil water at 100 degrees celsius in one atmosphere of pressure, the normal boiling point, we would wind up having a reversible process there...

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