MCAT Physics Question — Entropy Change

  • Reviewed By: Liz Flagge
  • 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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