Calculate ΔSrxn∘ for the reaction

2NO (g) + O2 (g) →2NO2 (g)

SubstanceS∘ (J/mol⋅K)

NO2240.0

O2205.2

NO210.8

What you need to do is like this:

ΔSrxn∘ = Products - Reactants

ΔSrxn∘ = [NO2 (mols*S∘) ] - [NO (mols*S∘) + O2 (mols*S∘) ]

ΔSrxn∘ = [ (2 mol * 240.0 J/mol*K) ] - [ (1 mol * 205.2 J/mol*K) + (2 mol * 210.8 J/mol*K) ]

ΔSrxn∘ = [480 J/K] - [626.8 J/K]

ΔSrxn∘ = - 146.8 J/K

I hope this is good for you