ShmoopTube

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And here's your Shmoop du jour, brought to you by the unbreakable second law of thermodynamics. [A boy practicing karate on a book of thermodynamics]

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Other unbreakable laws include: “Eat your vegetables” and “Sharing is caring.”

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Okay, here's today’s question.

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Which of the following would cause an increase in entropy?

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And here are our potential answers. [mumbling]

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By the way, that N.O. in answer D?

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Yeah, it’s not the opposite of “YES.” [A girl looking confused]

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It’s nitric oxide, people.

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That’s not to be confused with nitrous oxide, better known as laughing gas. [Students laughing in class and teacher asks what is funny]

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But who needs laughing gas when you’ve got us, and our dazzling sense of humor?

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Anyway, let’s get this thing going.

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To answer this question, we probably need to know what the heck entropy is.

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Well, according to the unbreakable second law of thermodynamics, the overall entropy [Image of a galaxy in a thermodynamics book]

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in the universe never decreases.

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Increasing entropy means a dispersal of energy or matter.

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This leads to increased disorder or messiness. [A boys bedroom door opens and lots of mess inside]

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So yes, your bedroom is messy and the Universe is, too.

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Try that one on Mom and Dad. Good luck!

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All right, we have to think about which of our answer choices describes an increase in

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disorder or dispersal.

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We know that the molecules in a gas are more spread out than in a liquid, and the molecules [Molecules in liquid bouncing up and down]

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in a liquid are more spread out than in a solid.

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The molecules in a gas are the most dispersed and most disordered…gases have the highest

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entropy.

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Okay, so let’s look at choice A. Freezing water represents a liquid to solid

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phase change, which corresponds to decreased disorder and thus decreased entropy. [Molecules inside an ice cube]

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So we can lose A. Those solid molecules sure are orderly, but

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jeez, they don’t have much fun.

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Could it be C - crystallization of salt from a supersaturated solution?

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Well, like freezing water, this answer describes a transition from the liquid phase to the [Molecules bouncing in a wine glass]

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solid phase, which corresponds to a decrease in disorder and thus a decrease in entropy.

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So say bye-bye to C. Choice D describes a reaction in the gaseous [Gaseous molecules in disorderly fashion]

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phase.

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We have two molecules combining to form one—matter that was once dispersed is now more compact.

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This is a decrease in disorder, and thus a decrease in entropy, and thus a decrease in

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our interest in choice D. That leaves us with choice B, boiling water. [A pan of boiling water]

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Boiling water represents a liquid to vapor phase change, which corresponds to increased

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disorder and thus increased entropy.

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That means that B is our answer.

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Hey, now that you know your second law of thermodynamics…maybe you could – we don’t

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know - clean your room? [boy using a vacuum in his room and mother watches]

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Just a thought.

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