ammonia gas reacts with oxygen as per the following rxn?

[Smooth Operater]

Q: ammonia gas reacts with oxygen as per the following rxn

4NH3 (g) + 3O2 (g) --> 6H2O (g) + 2 N2 (g)

dH, NH3 (g) = 11 Kcal/mole
dH, H2O (g) = 57.8 Kcal/mole

the above rxn is..

A. endothermic
B. exothermic



I say it is endothermic b/c when I go 6*57.8 - 4*11 , it gives me a positive dH for this rxn. But the actual answer is exothermic. Is my calculation wrong??

---

Members don't see this ad.

 

[Smooth Operater]

bump

 

[cranberryjuice]

Is this an example of a combustion reaction, which is by defintion an exothermic reaction? Not 100% sure though...