IB Physics Entropy Decrease

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A tutorial sheet on the entropy change in a rust reaction is given below. It is taken from Entropy and Rust by Daniel F Styer, Am J. Phys., 78 (11), November 2010, p 1077.

The rust reaction is 4Fe +3O2 →2Fe2O3. The entropy (at room temperature, 298.15 K and at a pressure of 105 Pa) of 1 mole of Fe is 27.280 JK-1, of 1 mole of O2 is 205.147 J K-1 and of one mole of Fe2O3 is 87.404 J K-1.

  1. Find the entropy change when 1 mole of Fe rusts.
  2. Describe the entropy change in the surroundings when 1 mole of Fe rusts.