Predict the sign of the entropy change, ΔS∘, for each of the reaction displayed.

Ba2+ (aq) + SO42- (aq) --> BaSO4 (s)

2NO2 (g) --> N2 (g) + 2O2 (g)

C5H12 (g) + 8O2 (g) --> 5CO2 (g) + 6H2O (g)

2NaClO3 (s) --> 2NaCl (s) + 3O2 (g)

2Na (s) + Cl2 (g) --> 2NaCl (s)

CH3OH (l) --> CH3OH (g)

(i)  ΔS° < 0 or negative

(ii) ΔS° > 0 or positive

(iii) ΔS° > 0 or positive

(iv) ΔS° > 0 or positive

(v) ΔS° < 0 or negative

(vi) ΔS° > 0 or positive

Explanation:

Entropy is a state function and extensive  property of the system.

It's the measurement of degree of randomness..

Entropy of the system decreases as follows

 Gas > Liquid > Amorphous solid > Crystalline solid.

In case for chemical reaction

 (i) Ba²⁺ (aq) + SO₄²⁻ (aq) --> BaSO₄ (s)

Total entropy change ΔS° < 0 or negative

During this reaction aqueous i.e liquid phase converted into solid phase.

So randomness  decreases and hence entropy also decreases.

(ii) 2 NO₂ (g) --> N₂ (g) + 2 O₂ (g)       ΔS° > 0 or positive

Since no. of gaseous moles increases from reactants to products.

(iii) C₅H₁₂ (g) + 8 O₂ (g) --> 5 CO₂ (g) + 6 H₂O (g)  ΔS° > 0 or positive

Since no. of gaseous moles increases from reactants to products.

(iv)   2 NaClO₃ (s) --> 2 NaCl (s) + 3 O₂ (g)  ΔS° > 0 or positive

Since no. of gaseous moles increases from reactants to products.

(v)  2 Na (s) + Cl₂ (g) --> 2 NaCl (s) ΔS° < 0 or negative

Since no. of gaseous moles decreases from left to right so entropy also decreases.

(vi) CH₃OH (l) --> CH₃OH (g)     ΔS° > 0 or positive

Because during this phase transition Liquid to gaseous randomness increases and hence entropy also increases.