# How to tell the difference between reversible and irreversible process

• PhyIsOhSoHard
In summary: The direction of heat flow can be reversed. Connecting a heat pump would cause heat to flow the other direction. But that would require more than just an infinitesimal change in conditions. So, your guess is correct, it is an irreversible process.
PhyIsOhSoHard
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?

PhyIsOhSoHard said:
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?
If it is reversible, the direction of the process can be reversed by an infinitesimal change in conditions. In the example you have given, half way through the process could you, by changing the conditions by the tiniest amount, make the heat flow back from the water into the steel block so that each reaches their initial states?

AM

Andrew Mason said:
If it is reversible, the direction of the process can be reversed by an infinitesimal change in conditions. In the example you have given, half way through the process could you, by changing the conditions by the tiniest amount, make the heat flow back from the water into the steel block so that each reaches their initial states?

AM

My guess is no because the steel block cannot spontaneously go back to 100 degrees celsius after it has been cooled so it is an irreversible process?

PhyIsOhSoHard said:
My guess is no because the steel block cannot spontaneously go back to 100 degrees celsius after it has been cooled so it is an irreversible process?
Why is it a guess? Just apply the principle stated in my previous post: can you reverse the direction of the process (heat flow from block to water) by an infinitesimal change of the initial conditions? The only conditions given are the temperatures of the block and water. If you changed those temperatures by the tiniest amount would the process (heat flow from block to water) reverse its direction?

AM

Andrew Mason said:
Why is it a guess? Just apply the principle stated in my previous post: can you reverse the direction of the process (heat flow from block to water) by an infinitesimal change of the initial conditions? The only conditions given are the temperatures of the block and water. If you changed those temperatures by the tiniest amount would the process (heat flow from block to water) reverse its direction?

AM

No you can not reverse the process so it is an irreversible process. Was that correct?

PhyIsOhSoHard said:
No you can not reverse the process so it is an irreversible process. Was that correct?
The direction of heat flow can be reversed. Connecting a heat pump would cause heat to flow the other direction. But that would require more than just an infinitesimal change in conditions. So, your guess is correct, it is an irreversible process.

AM

## 1. What is the definition of a reversible process?

A reversible process is one in which the system and its surroundings can be returned to their initial states after the process is completed, with no net change in the system or its surroundings.

## 2. What is an example of a reversible process?

An example of a reversible process is an ideal gas expanding and compressing in a piston-cylinder system, where the gas can be returned to its original state by reversing the direction of the piston.

## 3. How is a reversible process different from an irreversible process?

A reversible process is characterized by being able to be reversed without any net changes, whereas an irreversible process cannot be reversed without changes occurring in the system or its surroundings.

## 4. What are some indicators of a reversible process?

Some indicators of a reversible process include the absence of friction, constant pressure and temperature, and a slow and gradual change in the system.

## 5. How can you determine if a process is reversible or irreversible?

To determine if a process is reversible or irreversible, you can observe if the system and its surroundings return to their original states after the process is completed, and if the changes in the system and its surroundings are minimal or significant.

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