Answer:
The answer to your question is: ΔH = 1637.8
Step-by-step explanation:
Hess' law: This law states that the enthalpy change can be calculated even if it is not calculated directly.
"if a chemical change takes place by several routes, the overall enthalpy change is the same regardless the route".
Process
A) N2(g)+O2(g)—->2NO(g) Δ H= -180.5
B) N2(g) + 3H2(g) ——> 2NH3(g) Δ H= -91.8
C)2H2(g)+ O2(g) —-> 2H2O(g) Δ H= -486.6
The result must be:
4NH3(g)+5O2(g)—->4NO(g)+6H2O(g)
Turn letter B and multiply it by 2
4NH3 ⇒ 2N2 + 6H2 ΔH = 183.6
Multiply letter A by 2
2N2 + 2O2 ⇒ 4 NO ΔH = -361
Multiply letter C by 3
6H2 + 3O2 ⇒ 6H2O ΔH = -1459.8
Finally we add the equations up and simplify then:
4NH3 + 5O2 ⇒ 4NO + 6 H2O
And we add the ΔH = 183.6 - 361 - 1459.8
= -1637.8