Question

Select all of the following that you would predict to have a negative ΔS.

a) 2 NO2 (g) → N2 (g) + 2 O2 (g)

b) 2SO2 (g) + O2 (g) → 2 SO3 (g)

c) 2 C6H6 (l) + 15 O2 (g) → 12 CO2 (g) + 6 H2O (g)

d) 4 NO (g) + 6 H2O (g) → 4 NH3 (g) + 5 O2 (g)

e) 2 BF3 (g) + 3 CaO (s) → B2O3 (s) + 3 CaF2 (s)

f) 4 C (s) + S8 (s) → 4 CS2 (l)

g) O2 (g) → 2 O (g)

h) CuO (s) + H2 (g) → Cu (s) + H2O (l)

Answer 1

Answer – We are given the reactions and we need to look for the negative ∆S reaction.

We know the negative ∆S reaction is when the randomness of disorder decrease, means like phase goes to gas to liquid or liquid to solid. Or product as the fewer moles of gases than reactant then also there is negative ∆S reaction.

So the reaction – b, d, e and h

a) 2 NO2 (g) → N2 (g) + 2 O2 (g)

b) 2SO2 (g) + O2 (g) → 2 SO3 (g) This one has fewer moles of product.

c) 2 C6H6 (l) + 15 O2 (g) → 12 CO2 (g) + 6 H2O (g)

d) 4 NO (g) + 6 H2O (g) → 4 NH3 (g) + 5 O2 (g) This one has fewer moles of product.

e) 2 BF3 (g) + 3 CaO (s) → B2O3 (s) + 3 CaF2 (s) In this one phase gas, solid converted to solid and solid

f) 4 C (s) + S8 (s) → 4 CS2 (l)

g) O2 (g) → 2 O (g)

h) CuO (s) + H2 (g) → Cu (s) + H2O (l) In this one phase solid and liquid converted to solid and liquid