Chemistry Forum

Hello,

I really need help!! Any help will be greatly appreciated

I was given this data:

N₂ +O₂ --> 2 NO (delta) H = 180.7 kJ
2 NO + O₂ --> 2 NO₂ (delta) H = -150.3 kJ
2 N₂O --> 2 N₂ + O₂ (delta) H = -175.0 kJ

What is the (delta) Hrxn? using Hess' Law

N₂O + NO₂ --> 3 NO

(1) N₂ +O₂ --> 2 NO (delta) H₁ = 180.7 kJ
(2) 2 NO + O₂ --> 2 NO₂ (delta) H₂= -150.3 kJ
(3) 2 N₂O --> 2 N₂ + O₂ (delta) H₃ = -175.0 kJ

N₂O + NO₂ --> 3 NO H₄=?

To solve that you need to write this equation as a combination of equations with given H:
(3) => 2 N₂O = 2 N₂ + O₂
0.5*(3) => N₂O = N₂ + 0.5O₂
-0.5*(2) => NO₂ = NO + 0.5 O₂ (equation reversed because of -)
0.5*(3)-0.5*(2) => N₂O + NO₂ = N₂ + O₂ + NO
0.5*(3)-0.5*(2)+(1) => N₂O + NO₂ +N₂ + O₂ = 3NO +N₂ + O₂
After canceling out N₂ and O₂ on both sides of equations we have the required equation: N₂O + NO₂ = 3NO
Thus in according to Hess law:
H₄ = 0.5*H₃-0.5*H₂+H₁