Is the chemical bond formation an exothermic or a endothermic process? If it is an exothermic reaction, why energy is released again during bond breaking?

1 Answer
anor277
Aug 14, 2016

Bond breaking requires energy; bond making releases energy. This is a mantra you simply must learn.

Explanation:

We recognize that hydrocarbon combustion is an exothermic reaction:

#CH_4(g) + 2O_2(g) rarr CO_2(g) + 2H_2O(g)#

Looking at this reaction, clearly we have to BREAK strong #C-H# and #C-C# bonds in the hydrocarbon, and strong #O=O# bonds in the oxidant. Nevertheless, strong #C=O# and #O-H# bonds are FORMED; the balance between bond formation and bond breaking is the enthalpy associated with the reaction, and here the balance results in the RELEASE of energy.

Of course, by convention, if energy is released a negative sign is associated the term; #DeltaH# is negative.

Related questions
See all questions in Bonding
Impact of this question
7003 views around the world
You can reuse this answer
Creative Commons License