If the following reaction:
NO(g) + 1/2O2(g) ---- NO2(g)
has the following enthalpy change:
H° = -56 kJ/mol
What is the enthalpy of the decomposition reaction of 2 moles of NO2?

A. 56 kJ
B. 112 kJ
C. -56 kJ
D. -112 kJ

Question

If the following reaction: 
NO(g) + 1/2O2(g) ----> NO2(g)
has the following enthalpy change:
H° = -56 kJ/mol
What is the enthalpy of the decomposition reaction of 2 moles of NO2?

 		A.	56 kJ
 		B.	112 kJ
 		C.	-56 kJ
 		D.	-112 kJ

vera_ewing · Answer

I think the answer is D....

kainui · Answer

Well what if you reversed the arrow on the reaction? Then you would be going the opposite way right? That means instead of losing heat, which is a negative enthalpy change, you would be gaining heat, since it's the exact same thing going backwards! |dw:1421726425895:dw| Think of it like rearranging stuff, you can't create or destroy heat or atoms, so if you want to go backwards you need what you ended with and reverse it! |dw:1421726528184:dw|