Answer to Question #212131 in Civil and Environmental Engineering for syra

Question

Consider the formation of ammonia: N2(g) + 3 H2(g) 2NH3(g). (a). Assuming that H° and S° are constant with temperature, find the temperature at which Kp= 1.00.

(b). Find Kp at 400.0 °C, the typical temperature for NH3 production.

Answer 1

Part a

$N_2(g)+ 3 H_2(g) = 2NH_3(g)$

By using values of enthalpy and entropy from table

$∆H°rxn=2×∆Hf(NH_3)-3×∆Hf(H_2)-∆Hf(N_2)$

$∆H°rxn=2×-45.9-3×0-0$

∆H°rxn=-91.8 kJ/mol

$∆S°rxn=2×S°(NH3)-S°(N_2)-3×S°(H_2)$

$∆S°rxn=2×199-191.5-3×130.6$

$∆S°rxn=-197.3 J/K$

By using relationship

$∆H°-T∆S°=-RTLnKp$

Kp=1

$-91.8×10³+T×197.3=0$

$T=465.28 K$

Part b)

$At T=400°C=673 K$

∆H°-T∆S°=-RTLnKp

-91.8×10³-673×-197.3=-8.314×673×lnKp

$lnKp=-7.3245$

$K_p=6.592×10^{-4}$