Question

5. Predict which of the following reactions has a negative entropy change.

I. 2 HgO(s) → 2 Hg(l) + O2(g)

II. Ba2+(aq) + SO4 2-(aq) → BaSO4(s)

III. 2H2O2(l) → 2 H2O(l) + O2(g)

6. Predict which of the following reactions has a negative entropy change.

I. 2 SO2(g) + O2(g) → 2 SO3(g)

II. MgO(s) + CO2(g) → MgCO3(s)

III. PCl5(s) → PCl3(l) + Cl2(g)

Answer 1

5) Entropy is like randomness, the more molecules or moles you have, the more chances of random it can be. So, when you start off with two moles of reactants and end up making 3 as products, you've just increased the entropy, therefore, increasing randomness. And when entropy increases, the change in (delta)S is positive. A decrease in entropy yields a negative number.

II. Ba2+(aq) + SO4 2-(aq) → BaSO4(s) reaction has a negative entropy change.

6. The following reactions have a negative entropy change.

I. 2 SO2(g) + O2(g) → 2 SO3(g)

II. MgO(s) + CO2(g) → MgCO3(s)