How do exothermic reactions occur?

Answer 1

#|Enthalphy_(BondF)|#>#|Enthalphy_(BondB)|#

In any reaction, there is two stages. The Bond Breaking and Bond Forming stage which occurs after bond breaking.

Lets take #N_2 + 3H_2 = NH_3# as reaction for example. This reaction ,common in the Haber Process, is exothermic. Why? Simply , energy is first used to break the bonds of #N≡N# in #N_2# and #H=H# in #H_2#. Let this energy 'absorbed' be #|Enthalphy_(BondB)|# .

After that, free #N# atoms and free #H# atoms collide to form #N-H# single bonds in newly formed #NH_3#. Let this energy 'released' be #|Enthalphy_(BondF)|# .

Since in this reaction, the energy evolved(released) is larger than the energy absorbed to break the bonds, there is a net release of energy which results in the products having a lower energy content than the reactants as shown in the graph.

aka #|Enthalphy_(BondF)|# > #|Enthalphy_(BondB)|#

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Answer 2

Cooper Adams

Exothermic reactions occur when the overall energy of the products is lower than the energy of the reactants, resulting in the release of excess energy in the form of heat to the surroundings. This release of energy causes the surroundings to become warmer.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.