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Old Aug 8th 2018, 06:05 AM   #1
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Doubt with a calculation of the entropy of the surroundings.

If we have an exercise like this:

"Two moles of a perfect diatomic gas evolve from state 1 to state 2 through an irreversible process.
In this process, the gas starts from a molar volume of 0.04 m3 / mol and 100 K to have a temperature of 500 K keeping the pressure of the system constant. This process occurs between 2 heat sources, one of 100 K and another of 500 K.
Determine the entropy variation of the universe "

My problem is that when I do the entropy balance of the surroundings, I do not know what temperature to use for "the surroundings" since I have two heat reservoirs.

[NOTE] I know, this is not so advanced.
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Old Aug 9th 2018, 06:04 AM   #2
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Please Clarify your Description

I am having difficulty building a proper view of the scenario you are describing.

My attempt at re-describing the problem is:

You have a perfect diatomic gas in a container
You start with the gas at 100K and heat it to 500K
this container is such that it is free to expand while the temperature changes
thus keeping the gas at a constant pressure.

Is this what you are describing?
If not where is my misinterpretation?

An alternative interpretation might be:
you are passing the gas (through a pipe?) from a cold container to a hot container.

When you say "entropy variation of the universe" do you mean "entropy variation of the system"?
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Old Aug 9th 2018, 06:42 AM   #3
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Doubt with a calculation of the entropy of the surroundings.

Entropy is a state function of a system. That means you do not need to consider the surroundings.
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