What is the approximate value of log K_p for the reaction:
N₂(g) + 3H₂(g) ⇌ 2NH₃(g) at 25°C.
The standard enthalpy of formation of NH₃(g) is -40.0 kJ/mol and standard entropies of N₂(g), H₂(g) a

Question

What is the approximate value of log K_p for the reaction:
N₂(g) + 3H₂(g) ⇌ 2NH₃(g) at 25°C.
The standard enthalpy of formation of NH₃(g) is -40.0 kJ/mol and standard entropies of N₂(g), H₂(g) and NH₃(g) are 191, 130 and 192 JK⁻¹ mol⁻¹, respectively.

Prashant Kotian · Accepted Answer

Correct answer: D. ΔH°_rxn = 2(-40.0) = -80.0 kJ/mol = -80000 J/mol. ΔS°_rxn = 2(192) - 191 - 3(130) = 384 - 191 - 390 = -197 J/(K mol). ΔG° = -80000 - 298(-197) = -80000 + 58706 = -21294 J/mol. Using ΔG° = -2.303 RT log K_p, -21294 = -2.303(8.314)(298) log K_p. log K_p = 21294 / 5705.8 ≈ 3.73. Therefore, correct answer is D.

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