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Hi,

starting for this thread Question about entropy change in a reservoir consider the spontaneous irreversible process of heat transfer from a source ##A## at temperature ##T_h## to another source ##B## at temperature ##T_c## (##T_h > T_c##). The thermodynamic 'system' is defined from sources ##A## + ##B##. Since the process is not reversible, we can pick a reversible transformation between initial and final states to work out the entropy change between them (note that the entropy change is between the two states and it is

For instance we can introduce two other sources ##C##, ##D## at ##T_h## and ##T_c## respectively. Now let's take two isothermals: the first transfers heat ##Q## from source ##A## to ##C## both at temperature ##T_h## , the second transfers the same heat ##Q## from ##D## to ##B## both at temperature ##T_c##.

At the end of this process the 'system' as defined above is actually in the same state we get from the spontaneous irreversible process.

If the above is correct, I was thinking about the possibility of employ a Carnot cycle to 'implement' a reversible transformation to calculate the entropy change between initial and final 'system' states.

Does it actually make sense ? Thank you.

starting for this thread Question about entropy change in a reservoir consider the spontaneous irreversible process of heat transfer from a source ##A## at temperature ##T_h## to another source ##B## at temperature ##T_c## (##T_h > T_c##). The thermodynamic 'system' is defined from sources ##A## + ##B##. Since the process is not reversible, we can pick a reversible transformation between initial and final states to work out the entropy change between them (note that the entropy change is between the two states and it is

*not*a property of any transformation/process).For instance we can introduce two other sources ##C##, ##D## at ##T_h## and ##T_c## respectively. Now let's take two isothermals: the first transfers heat ##Q## from source ##A## to ##C## both at temperature ##T_h## , the second transfers the same heat ##Q## from ##D## to ##B## both at temperature ##T_c##.

At the end of this process the 'system' as defined above is actually in the same state we get from the spontaneous irreversible process.

If the above is correct, I was thinking about the possibility of employ a Carnot cycle to 'implement' a reversible transformation to calculate the entropy change between initial and final 'system' states.

Does it actually make sense ? Thank you.

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