Nitric oxide, NO, is able to combine with itself to from nitrous oxide, N_2O, an

Question

Nitric oxide, NO, is able to combine with itself to from nitrous oxide, N_2O, and oxygen, O_ 2. This reaction is represented by the following equation: 4NO(g) rightarrow 2N_2O(g) + O_2(g) given the following data, at 25 degree C, calculate for this reaction: a) the standard molar enthalpy of reaction, Delta_r H degree; b) the standard molar entropy of the reaction, Delta_r S degree; c) the standard Gibbs energy of reaction, Delta_r G degree at 37 degree C. d) Based on your answer in(c), is the reaction spontaneous or non-spontaneous at 37 degree C? e) What is the highest temperature at which this reaction is product favoured?

Explanation / Answer

Given reaction 4NO (g) -----------> 2N2O (g) + O2 (g)

a)

rHo = Hof of products - Hof of reactants

       = [ 2 x Hof N2O (g) + Hof O2(g) ] - [ 4 x  Hof NO(g)]     

       = [ 2 x 81.57 + 0] - [ 4 x 90.37 ] kJ/mol

       = -198.34 kJ/mol

  Ho = -198.34 kJ/mol = - 198340 J/mol

b) rSo

So = So of products - So of reactants

    = [ 2 x So N2O (g) + So O2(g) ] - [ 4 x So NO(g)]     

      = [ 2 x 220 + 205 ] - [ 4 x 210.6 ] kJ/mol

     = -197.4 J/mol/K

  So = -197.4 J/mol/K

c) Go

Given that temperature T = 37oC = 37 + 273 K = 310 K

Go = Ho - TSo

       = -198340 J/mol - [310 K x -197.4 J/mol/K]

       = -137146 J/mol

Go =  -137146 J/mol

d)

Since Go is negative, the reaction is spontaneous at 37oC.

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