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MCAT Question A Day - 4/2/14 - Answer!

For which of the gas-phase reactions below would DS be expected to be negative?

I. 2H2O → 2H2 + O2
II. 2H → H2
III. N2 + 3H2 → 2NH3

A.  I only
B.  II only
C.  I and II only
D.  II and III only

The correct answer is (D). In each of II and III, the number of moles of gaseous products is less than that of gaseous reactants; thus, “disorder” decreases.

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