Question

Calculate the free energy change for the reaction:

2 NO(g) + O2(g) → 2 NO2(g)
(A) - 9.3 kcal
(B) + 24.9 kcal
(C) + 9.3 kcal
(D) - 16.6 kcal
(E) + 16.6 kcal​

Answer 1

(D) - 16.6 kcal

Step-by-step explanation:

Hello,

In this case, the Gibbs free energy for the given reaction is computed in terms of the Gibbs free energy of formation of each species involved in the chemical reaction:

`\Delta _rG=2\Delta _fG_(NO_2)-2\Delta _fG_(NO)-\Delta _fG_(O_2)`

Thus, it is found for nitrogen monoxide, oxygen and nitrogen dioxide the following Gibbs free energies of formation: 87.6, 0 and 51.3 kJ/mol respectively, therefore we compute:

`\Delta _rG=2(51.3kJ/mol)-2(87.6kJ/mol)=-72.6kJ*(1kcal)/(4.184kJ) \\\\\Delta _rG=-17.35kcal`

The closest result is (D) - 16.6 kcal, as such difference is noticed when different sources for thermochemical data are used, in this case, the NIST data were used.

Best regards.