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

2SO2 (g) + O2 (g) - 2SO3 (g)
2NH3 (g) - N2 (g) + 3H2 (g)
2H2O2 (aq) - 2H2O (l) + O2 (g)
NaHCO3 (aq) + HCI (aq) - NaCl (aq) + H2O (l) + CO2 (g)

Question

Which of the following reactions results in a decrease in entropy?

2SO2 (g) + O2 (g) -> 2SO3 (g)
2NH3 (g) -> N2 (g) + 3H2 (g)
2H2O2 (aq) -> 2H2O (l) + O2 (g)
NaHCO3 (aq) + HCI (aq) -> NaCl (aq) + H2O (l) + CO2 (g)

anonymous · Answer

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mathmate · Answer

Add up the entropies of the reactants and those of the products. If the sum of entropies of the products is less than that of the reactants, there is a reduction. For the molar entropies of substances, see (third column, S): http://www2.ucdsb.on.ca/tiss/stretton/database/inorganic_thermo.htm