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Old Sep 30th 2017, 07:07 AM   #1
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Jigsaw puzzle and second law of thermodynamics.

I have read that when you decrease entropy somewhere it has to increase elsewhere. So when you put a jigsaw puzzle in order this decreases entropy of the puzzle but it should increase entropy elsewhere but where?

When you decrease the entropy of a system it should increase elsewhere but where, in case of jigsaw puzzle?
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Old Sep 30th 2017, 07:17 AM   #2
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Does entropy of the room increase?

If entropy decreases when we put the jigsaw puzzle in right order it has to increase elsewhere. So I think the entropy of the room as a whole increases with the jigsaw put in right order.
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Old Sep 30th 2017, 07:20 AM   #3
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Increased Entropy

You can make a part of the universe more ordered by doing a jigsaw puzzle, for instance. But you'll increase the overall entropy of the universe because of all the chemical energy you turned into heat moving your muscles around to pick the pieces up.
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Old Sep 30th 2017, 08:38 AM   #4
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You titled this question entropy and the Second Law.

So you presumably know what this law states.

So ask yourself

What is the heat exchanged?

If the answer is zero then the entropy change is also zero.

I will probably have to repeat this next bit in your other question, as I haven't looked at it yet.


The Second Law does not say entropy must increase.

It says that in an isolated system entropy can never decrease.

There is a difference.
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Old Oct 11th 2017, 12:34 AM   #5
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The room is not an isolated system.

You said that entropy can never decrease in an isolated system. So the fact that entropy has decreased when you clean your room or solve a jigsaw puzzle means that the room as a system is not isolated. So since the room is not isolated, the entropy can decrease.

Is this correct?
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Old Oct 11th 2017, 01:46 AM   #6
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Originally Posted by studiot View Post
You titled this question entropy and the Second Law.

So you presumably know what this law states.

So ask yourself

What is the heat exchanged?

If the answer is zero then the entropy change is also zero.

I will probably have to repeat this next bit in your other question, as I haven't looked at it yet.


The Second Law does not say entropy must increase.

It says that in an isolated system entropy can never decrease.

There is a difference.


Yes there is heat exchanged. By making your room tidy or solving a jigsaw puzzle, you are heating up the whole planet.

Your body sweats when you solve a jigsaw puzzle or tidy your room to release transfer heat from your body to Earth. The sweat evaporates and this is how your body moves heat from inside your body and transmits it to the environment (Earth).

When you heat up the whole planet, you are increasing the entropy. The increase in entropy is S=Q/T where Q is the heat your body emits and T is the Temperature of Earth.
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