Identifying endothermic and exothermic reaction

Asked Sep 04 '19 at 07:22

Active Sep 04 '19 at 07:59

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How can I know that a given reaction is endothermic or exothermic? I know that all combustion reactions are exothermic. But what about other reactions?

In my school exam I was asked about whether the reaction

$$\ce{N2 + O2 -> 2 NO}$$

is exothermic or endothermic. I didn't know that it is endothermic reaction and left that question. My teacher hence suggested me to learn all exothermic and endothermic reactions! Is it possible to do so? (Obviously not.) Please help me.

edited Sep 04 '19 at 07:59

andselisk

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asked Sep 04 '19 at 07:22

Divya Prakash Sinha

Exothermic or Endothermic reactions; Is the reaction exothermic or endothermic? – andselisk Sep 04 '19 at 08:02
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Well, you may learn just the endothermic reactions. The rest are exothermic. – Ivan Neretin Sep 04 '19 at 08:06
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If the product looks unfamiliar or you have trouble writing a nice all-octet Lewis structure (like you would have for NO), chances are the reaction is endothermic. You could memorize a table of bond dissociation energies for a more quantitative estimate, but maybe there are other things more worthwhile. – Karsten Sep 04 '19 at 10:04
Your teacher is being sarcastic. I am sure you have discussed this exact reaction in class, because you have to avoid that it runs in opposite direction during the Ostwald process when producing nitric acid. Because it is endothermic. Classic high school chemistry. – Karl Sep 04 '19 at 21:12
Another hint is, if you need high temperature for the reaction it is probably endothermic. – Fabian Sep 04 '19 at 21:21
Standard formation enthalpy of NO is ninety kJ/mol, of NO2 thirtyfour (at RT). – Karl Sep 04 '19 at 22:19

Identifying endothermic and exothermic reaction

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