Question

Since the computed value for AG is positive, the reaction is nonspontaneous under these conditions. Check Your Learning Calculate the free energy change for this same reaction at 875 °C in a 5.00 L mixture containing 0.100 mol of each gas. Is the reaction spontaneous under these conditions? ANSWER: AG +45.1 kJ/mol; no

Answer 1

2NH3 ----> N2 + 3H2 , Delta G° = 33 KJ/mol

[N2] = Moles/Volume = 0.100/5 = 0.02 M

[H2] = 0.10/5 = 0.02 M

[NH3] = 0.10/5 = 0.02 M

Reaction Quotient (Q) = [H2]^3 [N2] / [NH3]^2

Q = (0.02)^3 * (0.02) / (0.02)^2

Q = 0.0004 M

Temperature = 875°C = 875 + 273 = 1148 K

Now,

Delta G = Delta G° + RT lnQ

Delta G = 33000 + 8.314 * 1148 * ln (0.0004)

Delta G = -41676.4 J = -41.68 KJ/mol

Since, Delta G is negative; Reaction is spontaneous.

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