MCAT Physics Question — Entropy Change | Next Step Test Prep MCAT Physics Question — Entropy Change | Next Step Test Prep

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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

 

 

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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