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MCAT Physics Question — Entropy Change

At atmospheric pressure, carbon dioxide undergoes sublimation at -109.5°F. How does the entropy change when CO2 undergoes deposition?


A. ΔS>0

B. ΔS<0

C.  ΔS=0

D. cannot be determined

Click for Explanation

Deposition is a phase change from gas directly to solid. Less freedom of motion for the elements in a solid translates into less entropy: ΔS<0.


A. ΔS>0, incorrect, A solid arrangement of packed molecules is lower in probability than freely moving gas particles.

B. ΔS<0, correct.

C.  ΔS=0, incorrect, Gas phases have greater entropy than solid phases.

D. cannot be determined, incorrect, See answer C.

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