Question

Which of the following reactions results in a decrease in entropy?

Answer 1

6CO2 (g) + 6H2O (l) arrow C6H12O6 (s) + 6O2 (g)
2NH3 (g) arrow N2 (g) + 3H2 (g)
N2O4 (g) arrow 2NO2 (g)
2H2O2 (aq)arrow 2H2O (l) + O2 (g)

Answer 2

I'd say the first one.
Entropy is the measurement of disorder in a system. Gases have higher entropy than liquids, which have higher entropy than solids. Also, as the number of moles increases from reactants to products, the entropy increases (and it decreases when # of moles decrease from reactants to products).

In the first equation, you have 12 moles in the reactants and 7 in the products. And there is a liquid to solid switch. Definitely the answer.

Answer 3

Ohhhh, yeah that makes sense. :)