Question

What is the standard enthalpy of formation of nh3 gas, standard heat of atomisation of nh3(g), h2(g) and n2(g) are 1167 kj/mol and 942 kj/mol respectively?

Answer 1

The standard enthalpy of formation of NH3 is -46.0 kJ mol-1.

Answer 2

Answer:

-42 kJ/mol is the standard enthalpy of formation of ammonia gas

Explanation:

$NH_3(g)\rightarrow N(g)+3H (g),\Delta H_{atom,1}=1167 kJ/mol$..[1]

$H_2(g) \rightarrow 2H (g),\Delta H_{atom,2}=436 kJ/mol$..[2]

$N_2(g)\rightarrow 2N (g),\Delta H_{atom,3}=942  kJ/mol$..[3]

$\frac{1}{2}N_2 (g)+\frac{3}{2}H_2 (g)\rightarrow NH_3 (g),\Delta H =?$..[4]

(1/2)[3]+ (3/2) × [2] - [1] = [4] (Using Hess's law)

$\Delta H=\frac{1}{2}\times 942 kJ/mol+\frac{3}{2}\times 436kJ/mol-1167 kJ/mol$

$=-42 kJ/mol$

-42 kJ/mol is the standard enthalpy of formation of ammonia gas