-CORRECTION-

Question

N2 + O2 --> 2 NO change in heat (delta H)= 43.2 kcal

based on the reaction, which statement is true?
a) 43.2 kcal are consumed when 1.00g of O2 reacts
b) 43.2 kcal are consumed when 1.00g of N2 reacts
c) 43.2 kcal are consumed when 1.00g of NO is produced
d) 43.2 kcal are consumed when 1.00 mole of O2 reacts

I think it is D because the heat is used when the reaction occurs and the product is made. Is this correct?

***I actually meant to write C not D. When I copied the question over from my worksheet there were 5 answers and I took one out because I knew it was not correct and I accidentally wrote the letter for the answer on my paper and not what I wrote on here.

What I was trying to say for my reason is that the energy is not used until the two products react together to form 2 NO. So when 2 NO is produced, the energy is released. None of the possible answers say when they both react so that's why I thought it would be the product. But I really don't know. I just don't understand Chemistry. So if it is actually D, what is the reason?

Answer 1

The FIRST think you need to understand about chemistry is that the reaction is not between grams but between moles. Let me point out some things that are common to all the answers. The delta H is positive which means that the reaction is endothermic (heat is consumed in the reaction) so nothing can be eliminated on that point. Answers a, b, and c are wrong because they have grams in them. D is the only answer that uses moles; therefore, D is correct. So when 1 mole N2 reacts with 1 mole of O2 to form 2 moles NO, 43.2 kcal are consumed. As for both reactants not being used in the answer consider that IF 1 mole O2 is consumed then 1 mole N2 MUST have been consumed also AND 2 moles NO must have been produced. But the secret to the answer (from those you listed since I don't know the one you didn't post) is that D is the only one that lists moles.

Answer 2

I wanted to point out in your clarified explanation that when 2 NO moles are produced, the energy is NOT released. It is CONSUMED.