(40 pts) Temperature Impact on Free Energy Given the following reaction: NO2 (g)

ID: 636054 • Letter: #

Question

(40 pts) Temperature Impact on Free Energy Given the following reaction: NO2 (g) + N2O (g) ? 3 NO (g)

(a) Use Appendix B (pg. A 5-7) and Table 20.1, pg. 832 to predict how ?G° for the reaction varies with increasing temperature

NO2-delta Hf: 33.2 delta S: 239.9

N2O- delta Hf: 82.05 delta S: 219.7

NO- delta Hf: 90.29. delta S: 210.65

(b) Calculate ?G° at 800 K, assuming that ?Ho and ?So do not significantly change with temperature

(d) Is the reaction more or less spontaneous at 1000 K than at 800 K ?

a) The reaction is

NO2(g) + N2O(g) ========== 3NO(g)

Delta H(rxn) = Delta H(products) - Delta H(reactants)

=> 3 * Delta H(NO2) - Delta H(N2O) - Delta H(NO2)

=> 3 * 90.29 - 82.05 - 33.2

=> 155.62 kJ

Delta S(rxn) = Delta S(products) - Delta S(reactants)

=> 3 * Delta S(NO2) - Delta S(N2O) - Delta S(NO2)

=> 3 * 210.65 - 219.7 - 239.9

=> 172.35 J/K

Since Delta S is positive, hence with the increasin in temperature Delta G will become more negative and reaction will be stable

Delta G(800) = Delta H - T * Delta S

=> 155.62 kJ - 800 * 0.17235 kJ

=> 17.740 kJ

Delta G(100) = Delta H - T * Delta S

=> 155.62 kJ - 1000 * 0.17235 kJ

=> -16.73 kJ

d) The reaction is more spontaneous at 1000K, since Delta G is negative at 1000K

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