Irreversible process Entropie-Change/cylinder

In summary, the difference in the equations for entropy change in an irreversible process and a reversible process is due to the nature of the closed system being considered. The inequality applies to irreversible processes while the equality applies to reversible processes. The heat reservoir can be considered a separate system in the reversible process, with its own change in entropy.
  • #1
Abigale
56
0
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
 
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  • #2
Your inequality applies to the closed system that you are applying the process to. Your second equation is not the entropy change for the material in the cylinder unless the process is reversible, irrespective of the heat reservoir. If you regard the heat reservoir as a system, then the second equation describes its change of entropy, since its temperature is constant and (virtually) uniform, and the heat addition takes place reversibly. The key to inequality vs equality is if the system under consideration is undergoing a reversible change.
 

Related to Irreversible process Entropie-Change/cylinder

1. What is an irreversible process?

An irreversible process is a physical or chemical change that cannot be reversed or undone. This means that once the process has occurred, it cannot be returned to its original state.

2. How does the entropy change in an irreversible process?

In an irreversible process, the entropy of the system always increases. This is because irreversible processes are associated with an increase in disorder or randomness in the system, which is reflected in the increase in entropy.

3. What is the relationship between entropy change and a cylinder?

In a cylinder, the volume remains constant while the pressure and temperature may change. This can lead to an irreversible process, where the entropy of the system increases.

4. Can the entropy change in an irreversible process be calculated?

Yes, the entropy change in an irreversible process can be calculated using the formula ΔS = Q/T, where Q is the heat transferred and T is the temperature.

5. What are some examples of irreversible processes?

Examples of irreversible processes include combustion, diffusion, and irreversible chemical reactions. Other examples include the expansion of a gas into a vacuum and the mixing of two different substances.

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