Given the following information: 2NO(g)==> N2(g)+O2(g) ^H= -180.6 kj , N2(g)+O2(g) + CI2(g)==>2NOCI(g). , ^H = +103.4 kj. Find the ^H of the following reaction: 2NOCI(g)==>2NO(g)+CO2(g)

Answer 1

The target reaction is... 2NOCl(g) ==> 2NO(g) + Cl₂(g) [note: you gave an incorrect equation]

We will use Hess' Law to find the ∆H of this target reaction using the other 2 reactions that are given,.

(1) 2NO(g) ==> N₂(g) + O₂(g) ∆H = -180.6 kJ

(2) N₂(g) + O₂(g) + Cl2(g) ==> 2NOCl(g) ∆H = +103.4 kJ

reverse eq.(1): N2(g) + O2(g) ==> 2NO(g) ∆H = +180.6 kJ (note the change in sign)

reverse eq.(2): 2NOCl(g) ==> N₂(g) + O₂(g) + Cl₂(g) ∆H = -103.4 (note the change in sign)

add these together and cancel like items on each side to get...

2NOCl(g) ==> Cl2(g) + 2NO(g) and this is the desired target equation from above.

We then have to add the corresponding ∆H values...

+180.6 kJ - 103.4 kJ = 77.2 kJ