Absolute Entropy and Entropy Change

AP Chemistry· difficulty 2/5

Standard entropies (J/mol·K) for the reaction 2 H₂(g) + O₂(g) → 2 H₂O(g) are tabulated.

Substance S° (J/mol·K) H₂(g) 131 O₂(g) 205 H₂O(g) 189

What is ΔS° for the reaction?

  • A

    −151 J/mol·K

  • B

    +89 J/mol·K

  • C

    +151 J/mol·K

  • D

    −89 J/mol·K

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Explanation

ΔS° = 2(189) − [2(131) + 205] = 378 − (262 + 205) = 378 − 467 = −89 J/mol·K.

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