Chemical EquilibriumMedium

Question

What is the approximate value of log KP for the following reaction?

N2(g) + 3H2(g) $\rightleftharpoons$ 2NH3(g) at 25°C. The standard enthalpy of formation of NH3(g) is −40.0 kJ/mol and the standard entropies of N2(g), H2(g) and NH3(g) are 191, 130 and 192 JK–1 mol–1, respectively.

Options

A.0.04
B.7.05
C.8.6
D.3.73

Solution

For the given reaction, ΔH° = 2 × (–40) = –80 KJ

and ΔS° = (2 × 192) – (191 + 3 × 130) = –197 J/K

Now, ΔG° = ΔH° – ΔS° = –2.303 RT log K°p

$\therefore\log K_{p} = \frac{( - 80 \times 1000) - 298 \times ( - 197)}{( - 2.303 \times 8.314 \times 298)} = 3.73$

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