Thethermodynamic properties for a reaction are related by the equationthat defin

Question

Thethermodynamic properties for a reaction are related by the equationthat defines the standard free energy, Change in G, in kJ/mol:

Change in G = change in H – T change in S

where change inH is the standard enthalpy change in kJ/mol and change in S orentropy is the standard entropy change in J/mol * K. A goodapproximation of the free energy change at other temperatures

Change in freeenergy or G, can also utilize this equation by assuming enthalpy(Change in H) and entropy (Change in S) change little withtemperature.

For the reactionof oxygen and nitrogen to form nitric oxide, consider the followingthermodynamic data:

Change in H reaction

180.5 kj/mol

Change in S reaction

24.8 J/mol * K

The standardfree energy change G and the equilibrium constant K for a reactioncan be related by the following equation:

Change of G = -RTInK

where T is theKelvin temperature and R is equal to 8.314J/(mol*K).

Calculate theequilibrium constant for the reaction forming nitric oxide at roomtemperature, 25 C.

Could youexplain once you get down to InK = -68.62 how you find K.

Change in H reaction

180.5 kj/mol

Change in S reaction

24.8 J/mol * K

Explanation / Answer

We Know that :      The given Reaction is :         N2 + O2 ------> 2NO       G reaction = G products - Greactants                            =   2 x 86.55 kJ - [ 0 + 0 ]                             =  173.1kJ          G = -RT lnK         -173.1x103 J = 8.314 J / mol-K x 298 K xlnK           lnK = -69.866           Takingthe inverse logtharim both sides we get :                K = 4.59 x 10-31

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