Question

All the oxides of nitrogen have positive values of G at 298K but only one common oxide of nitrogen has a positive S identify that oxide of nitrogen without reference to thermodynamic data

Answer 1

The common oxide of nitrogen that has a positive ΔS°f is nitric oxide (NO)

Step-by-step explanation:

Without reference to thermodynamic data, we have;

1) N₂ (g) + O₂ (g) ⇄ 2 NO (g)

1 unit of N₂ + 1 unit of O₂ (total of 2 units) gives 2 units of NO, (Increase of +0 disorder)

∴ΔS°f = +ve

2) 2NO + O₂ → 2NO₂

2 unit of NO + 1 unit of O₂ (total of 3 units) gives 2 units of NO₂, (Decrease of disorder)

∴ΔS°f = -ve

3) N₂ + 1/2 O₂ → N₂O

1 unit of N₂ + 1/2 unit of O₂ (total of 1+1/2 units) gives 2 units of NO₂, (Decrease of disorder)

∴ΔS°f = -ve

4) 4 NO₂ + O₂ → 2N₂O₅

4 unit of NO₂ + 1 unit of O₂ (total of 5 units) gives 2 units of N₂O₅, (Decrease of disorder)

∴ΔS°f = -ve

5) NO + NO₂ ⇄ N₂O₃

1 unit of NO + 1 unit of NO₂ (total of 2 units) gives 1 unit of N₂O₃, (Decrease of disorder)

∴ΔS°f = -ve

Therefore, the common oxide of nitrogen that has a positive ΔS°f without reference to thermodynamic data is nitric oxide NO.