Sort each claim by whether the second law of thermodynamics permits it.
Groups: Permitted · Forbidden
- A sealed flask tidies itself up, ending more ordered than it began
- Heat flows on its own from a cold block into a hotter block touching it
- A crystal forms, lowering local entropy while releasing heat that raises it elsewhere
- A refrigerator cools its interior while warming the kitchen
Hints
- The second law constrains the TOTAL entropy of an isolated system, not the entropy of one part of it.
- Local order is allowed provided disorder increases somewhere else by at least as much.
Show the answer
Permitted: A refrigerator cools its interior while warming the kitchen, A crystal forms, lowering local entropy while releasing heat that raises it elsewhere
Forbidden: Heat flows on its own from a cold block into a hotter block touching it, A sealed flask tidies itself up, ending more ordered than it began
Fridges and crystals lower entropy locally while dumping more entropy into their surroundings, so the total still rises. What is forbidden is a decrease in the total, spontaneous heat flow up a temperature gradient, or a perfect heat-to-work engine. Reading the second law as 'order is impossible' is the misconception it corrects.
Practise Thermodynamics and Statistical Ideas
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More questions on Thermodynamics and Statistical Ideas
- Complete the statistical reading of the second law.
- Order the statistical argument for why an isolated gas spreads out.
- The second law says entropy tends to increase, yet nothing in Newton's laws forbids a broken cup…
- A fridge cools its contents while making the kitchen warmer overall. Why does that not violate the second law?