Chemical thermodynamics


Hess's law

Exercise 8

     


 

Will the following synthesis of ammonia
$2N_2(g)+6H_2O(g)$ → $3O_2(g)+4NH_3(g)$
be economically intelligent ?

(a)  $NH_3(g)$ → $\frac{1}{2}N_2(g)+\frac{3}{2}H_2(g)$  |  $\Delta H_a = 46 \;kJ$
(b)  $\Delta H_c (C_2H_2)= -1299 \;\frac{kJ}{mol}$  |  $\Delta H_b = -484\; kJ$


-4(a)   $2N_2(g)+6H_2(g)$ → $4NH_3(g)$  |  $-4\Delta H_a$
-3(b)   $6H_2O(g)$ → $6H_2(g)+3O_2(g)$ → $6CO_2(g)+3H_2O(l)$  |  $-3\Delta H_b$


-4(a)-3(b)   $3C_2H_2(g)+\frac{15}{2}O_2(g)$ → $6CO_2(g)+3H_2O(l)$&$2N_2(g)+6H_2(g)$+$6H_2O(g)$ → $4NH_3(g)$+$6H_2(g)+3O_2(g)$nbsp; |  $-4\Delta H_a-3\Delta H_b$
(c)=-4(a)-3(b)   $2N_2(g)+6H_2O(g)$ → $3O_2(g)+4NH_3(g)$  |  $\Delta H_c$ = $-4\Delta H_a-3\Delta H_b$ = $1268\;kJ$


The heat that must be provided is much to important!