What is the sign of ΔS° for this reaction?

Answer: Negative; gas moles decrease and form a liquid Going from 3 mol gas to 2 mol liquid sharply reduces disorder; ΔS° < 0.

The second law states that for a spontaneous process

Answer: ΔSuniverse 0 Total entropy of universe increases for any spontaneous process.

Heat flowing from hot to cold reservoir

Answer: Increases ΔSuniverse |ΔScold| (gain at low T) exceeds |ΔShot| (loss at high T), giving net ΔS 0.

AP Chemistry · Topic 9.1

Introduction to Entropy Practice

Q: The second law states that for a spontaneous process

Answer: ΔSuniverse 0 Total entropy of universe increases for any spontaneous process.

Q: Heat flowing from hot to cold reservoir

Answer: Increases ΔSuniverse |ΔScold| (gain at low T) exceeds |ΔShot| (loss at high T), giving net ΔS 0.

Part of Applications of Thermodynamics.(ENE-4.A)

Practice questions

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Sample questions

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Sample 1difficulty 2/5
$What is the sign of ΔS° for this reaction?$
- A
  $Cannot be determined$
- B
  $Positive; products are simpler$
- C
  $Negative; gas moles decrease and form a liquid$
  check_circle
- D
  $Zero$
Why
$Going from 3 mol gas to 2 mol liquid sharply reduces disorder; ΔS° < 0.$
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Sample 2difficulty 2/5
$The second law states that for a spontaneous process$
- A
  $ΔH < 0$
- B
  $ΔS_surr > 0$
- C
  $ΔS_sys > 0$
- D
  $ΔS_universe > 0$
  check_circle
Why
$Total entropy of universe increases for any spontaneous process.$
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Sample 3difficulty 3/5
$Heat flowing from hot to cold reservoir$
- A
  $Has ΔS_universe = 0$
- B
  $Violates first law$
- C
  $Decreases ΔS_universe$
- D
  $Increases ΔS_universe$
  check_circle
Why
$|ΔS_cold| (gain at low T) exceeds |ΔS_hot| (loss at high T), giving net ΔS > 0.$
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Sample 4difficulty 4/5
$The second law of thermodynamics states that for spontaneous processes$
- A
  $_{system}$
- B
  $ΔH < 0 always$
- C
  $_{universe}$
  check_circle
- D
  $Energy is destroyed$
Why
$Total entropy of universe must increase. The system can have decreasing entropy if surroundings increase by more (e.g., freezing water releases heat to surroundings).$
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Sample 5difficulty 4/5
$For a reversible process, ΔS_universe is$
- A
  $Negative$
- B
  $Zero$
  check_circle
- C
  $Infinite$
- D
  $Positive$
Why
$Reversible = idealized, so ΔS_universe = 0; real (irreversible) gives > 0.$
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