HW#6.3 If the reaction

$$\ce{Fe2N(s) + 3/2 H2(g) <=> 2 Fe(s) + NH3(g)}$$

comes to an equilibrium at a total pressure of $\pu{1 bar},$ analysis of the gas shows that at $\pu{700 K}$ and $\pu{800 K},$ $p_\ce{NH3}/p_\ce{H2}$ are $2.165$ and $1.083,$ respectively, if only $\ce{H2(g)}$ was initially in the gas phase and $\ce{Fe2N(s)}$ was in excess:

a. Calcualte $K_p$ at $\pu{700 K}$ and $\pu{800 K}.$
b. Calculate $Δ_\mathrm{r}S^\circ$ at $\pu{700 K}$ and $\pu{800 K}$ and $Δ_\mathrm{r}H^\circ$ assuming that it is independent of temperature.
c. Calculate $Δ_\mathrm{r}G^\circ$ for this reaction at $\pu{298 K}.$

At first I ignored the excess data, then I assumed that the pressure exerted by the solids is null and adding partial pressures I got an answer (sum of pressure of gases equals 1).

The problem is that part a in the book gives answer $K_p = 1.777$ at $\pu{700 K}$ which I think is wrong. Please help.

  • 1
    $\begingroup$ I get 3.85 at 700K $\endgroup$ – Chet Miller Sep 3 at 18:29
  • $\begingroup$ I got that too but the book says 1.777 guess I can't trust the back of the book now ,using Castellan Physical Chemistry $\endgroup$ – Esteban Soto Montijo Sep 3 at 19:42

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