Entropy question....

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catzzz88

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A block of ice is reduced in temperature from -5 C to -10 C. As a consequence, which of the following is true?

A. The entropy of the block of ice has increased.
B. The total entropy of the universe has increased.
C. The temp. of the air surrounding the block of ice has decreased.
D. The average kinetic energy per molecule of the water has increased.

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B - it's always correct, anyway.

A - decrease of temperature generally is associated with decrease of entropy, not increase.
C - to cool down the ice block, the media around it must have been colder than its current temperature - the ice cooled, the air warmed up.
D - lower temperature will correspond to lower average energy.
 
Kaplan says "the universe must pay the price; since the process isn't reversible, the entropy of the universe must increase."

1) How do we know that it is an irreversible process?

2) Isn't the block of ice inherently included in the set called "universe"? Even if the universe compensates, wouldn't that just lead to no entropy change in the said "universe"?

3) With no other information, should we just assume that laws of thermodynamics are being tested and say "Yes, B must be the answer because the entropy of the universe is ALWAYS increasing"?


Waahhhh.... Thanks for all help!
 
B is the answer since the temp of the ice decreases from -5 to -10, there is a decrease of entropy of the ice...If the entropy of the ice decreases; consequently, the entropy of the universe (or surrounding) increases. You can answer that question by process of elimination as milski said because the other choices are blatantly false.
 
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Temp101 accurately sums it up, if it's cooling down the entropy of the object has decreased. That decrease has to come somewhere, so the universe' (environment) increases!
 
The universe does include the ice block - if its entropy increases or decreases does not matter. From second law of thermodynamics, its entropy will increase. "Surroundings" is what you would use for anything but the block.

Don't worry about reversible processes, especially when they're not explicitly mentioned - they are only an idealization. All real world macro processes are irreversible. Even in that case, ΔS=0, not negative.
 
So I guess I am getting confused about what is meant by "Universe"

If they mean "surroundings," why dont they just say that? Universe includes the ice block and even if the universe is compensating, the net entropy change would be zero (ignoring laws of thermodynamics).

If they mean "surroundings" then yes the net entropy of surroundings will increase...

Maybe I just need to stop over-thinking and just move on, but this one bugs me.
 
So I guess I am getting confused about what is meant by "Universe"

If they mean "surroundings," why dont they just say that? Universe includes the ice block and even if the universe is compensating, the net entropy change would be zero (ignoring laws of thermodynamics).

If they mean "surroundings" then yes the net entropy of surroundings will increase...

Maybe I just need to stop over-thinking and just move on, but this one bugs me.

That's the whole point - you cannot ignore the laws of thermodynamics. They could re-write the question as "Something happened.". B would still be the correct answer.
 
If a system loses entropy then doesn't the surroundings which i.e. the universe have to gain it?

surroundings != universe
system+surroundings=universe.

Otherwise, you're correct - when the entropy in a system decreases, the surroundings' entropy will increase in a way that the total entropy of the universe will increase as well.
 
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