Question

For which one of the following reactions is ASº negative? Select one: O a. 3 H2(g) + Fe2O3(s) → 2 Fe(s) + 3 H2O(g) O b. (NH4)2CO3(s) + 2 NH3(g) + H2O(g) + CO2(g) O c. 2 NO2(g) → N2(g) + 2 O2(g) O d. 2 IBr(g) → Iz(s) + Brz(4) o e. CoH6(s) → CoH6()

Answer 1

dS° = entropy of products - entropy of reactants.

If no. Of molecules on the product side is more than number of molecules on reactant side , then dS° will be positive .

And if number of molecules on the product side is less than number of molecules on reactant side , then dS° will be negative.

Thus only in case of (d)

2IBr(g) -----> I2(s) + Br2(l) , there will be dS° negative.

Although number of molecules on both side is same , but here a gaseous substance is changing into solid and liquid material , and entropy of gases is more than solid and liquid.  

Thus entropy change in case of (d) will ne negative.

Option (d) is the correct answer.

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