For Questions 23-27, refer to these reactions: a. 4NH, (g) +5O, (g) 4NO (g) +6H,
ID: 1031433 • Letter: F
Question
For Questions 23-27, refer to these reactions: a. 4NH, (g) +5O, (g) 4NO (g) +6H,O (g) b. 3NO2 (g) + H2O (l)--2HN03 (l) + NO (g) c. 2NH,NO, (s)2N, (g) + O, (g+4H,O (g) 023. Calculate the standard change in enthalpy () for each reaction, and tell whether each reaction is endothermic or exothermic. 024. Calculate the standard entropy change (AS9) for each reaction. O 25. Calculate the change in free energy (AG) for each reaction at 25.0 °C, and tell whether each reaction is favorable (spontaneous) or unfavorable (nonspontaneous) at this temperature. O 26, Calculate G for each reaction at 1000, K, and tell whether 0 27. Calculate the temperature (if any) at which each reaction DS O 28. How is developing an ice pack obeying two important each reaction is favorable (spontaneous) or unfavorable (nonspontaneous) at this temperature. changes from being spontaneous to nonspontaneous (the temperature at which AG equals zero). commands from God?Explanation / Answer
The change in free energy for any reaction is given as :
G0(rxn)=G0f(products)G0f(reactants)
a) 4NH3 (g) + 5O2 (g) --------------> 4NO (g) + 6H2O (g)
G0(rxn) = 4* G0f NO + 6* G0f H2O (4* G0f NH3 + 5 *G0f O2)
G0(rxn) = 4*(86.57) + 6*(-228.59) - 4*(-16.48) -5*(0)
G0(rxn) = 346.28 -1371.54 +65.92 = -959. 34 KJ/mol
The reaction is spontanneous as the change in gibbs free energy is -ve.
b) 3NO2 (g) + H2O (l) -------------> 2HNO3 (l) + NO (g)
G0(rxn) = 2* G0f HNO3 + G0f NO (3* G0f NO2 + G0f H2O)
G0(rxn) = 2* (-79.91) + 86.57 - 3* (51.30) + 237.18
G0(rxn) = -159.82 + 86.57 - 153.9 + 237.18
G0(rxn) = 10.03 KJ/mol
The reaction is non spontanneous as the change in gibbs free energy is +ve.
c) 2NH4NO3 (s) -------------> 2N2 (g) + O2 (g) + 4H2O (l)
G0(rxn) = 2* G0f N2 + G0f O2 +4* G0f H2O - 2* G0f NH4NO3
G0(rxn) = 2* 0+ 0+4* (-237.18) - 2* (-184.01)
G0(rxn) = 4* (-237.18) - 2* (-184.01)
G0(rxn) = -580.7 KJ/mol
The reaction is spontanneous as the change in gibbs free energy is -ve.
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