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question “If I clean my room, it will become more ordered and I will be breaking...
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The second law of thermodynamics states that the entropy of an isolated system never decreases. This means that chance in entropy is never negative: `\Delta S >= 0` .
In your problem, your argument is that since cleaning the room results into an ordered state (of the room), then the process must be a violation of the law of thermodynamics. If we define the room as the entirety of the system already, then it's obviously impossible that it will spontaneously become ordered (or that it will spontatneously clean itself on its own). This happening (the room cleaning itself) is the violation of the second law. However, this is not the case. Clearly, someone cleaned the room (in this case, you did!). Hence, you must be part of the system. This means that if we are calculating entropy, we are not only concerned with the state of disorderliness (or state of order) of the room, but rather the room plus the cleaner (you!). In this case, we are not violating the second law of thermodynamics...
It is true that the degree of disorder of the room is decreased - that is, it's entropy decreased. However, it's not isolated (not the entire system) -- which means that somewhere else, entropy must have increased to compensate for the order of the room. This something else is you. In cleaning your room, you are using energy. This energy is essentially from the food you eat. The food you eat was ordered -- probably large molecules. As you digested them, you broke them down into smaller pieces -- this is an increase in entropy. Further breaking down, means higher entropy. Then you used energy -- and most probably heat dissipated in the process. Heat is the most disordered form of energy. Hence, while the room had `\DeltaS<0` , your body, through digestion, and use of energy has `\DeltaS>0` and this compensates for the loss of disorder of the room.
If you think about it, this is not very different from development of a living organism -- say for instance, a plant. A plant (or any living organism) is obviously very organized, and yet, in a universe which is governed by the law of thermodynamics (focus on 2nd!), we exist, plants exist. This is because while we develop and maintain order in our body, we consume things, break them down, constantly using them for our good (e.g. food) -- and eventually, when we fail to do so, we die; and left alone, we disintegrate (increase in entropy!).
In the end, simply note that in using the 2nd law of thermodynamics one must define what a system is. A room alone cannot become clean. But if we add another element to the system (you) an increase in the entropy in one part, could compensate for the loss in another. Broadly, the universe as an isolated system has a positive entropy all the time -- which means if something comes to order in one part, there must have been something else that happened elsewhere (more disorder) to allow this to happen.
Posted by mvcdc on July 11, 2013 at 1:58 PM (Answer #1)
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