Question

Nitric oxides, NO and NO2, contribute to air pollution, acid rain, and the depletion of the ozone layer. After NO forms in the combustion chamber of an automobile engine, it reacts further with oxygen to form NO2. The reaction is given by

2NO(g)+O2(g)→2NO2(g)

The following table gives some entropy values:

Substance	ΔS∘ (J/mol⋅K)
NO2	240.0
O2	205.2
NO	210.8

Calculate delta S_RXN for the reaction

Answer 1

2NO(g)+O₂(g)→2NO₂(g) : ΔS_rxn = ?

ΔS_rxn = ΔS⁰_products – ΔS⁰_reactants

ΔS_rxn = [(2x ΔS⁰_NO2(g) ) ] - [( 2 x ΔS⁰_NO(g) )+ ( ΔS⁰_{O2 (g)} )]

        = [(2x240.0)] - [(2x210.8)+205.2 ]

        = -146.8 J/(mol-K)

Therefore ΔS_rxn = -146.8 J/(mol-K)