Why is bond formation exothermic

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Learn more. Is Bond Formation "Strictly" Exothermic? Ask Question. Asked 7 years, 5 months ago. Active 3 years, 10 months ago.

Viewed 7k times. Improve this question. Dissenter Dissenter Add a comment. Active Oldest Votes. Improve this answer. Community Bot 1. How can non-bonded elements have "dissociation" energies? There are weaker forces at play, i. London Dispersion and van der Waals. These are also part of the reason, why noble gases can be liquid close to zero Kelvin. Here you are comparing methane to methyl radical and hydrogen radical, which is a specific reaction.

Weak bonds do form between noble gas atoms: scitation. For an exothermic reaction, the enthalpy change is always negative.

In an endothermic reaction, the products are at a higher energy than the reactants. Energy changes Breaking and making bonds During a chemical reaction: bonds in the reactants are broken new bonds are made in the products Energy is absorbed to break bonds. Usually an exothermic reaction corresponds to the breaking of weak bonds with small bond enthalpies and the making of strong bonds with large bond enthalpies.

The combustion of methane discussed in Example 1 from Bond Enthalpies is another example of the formation of stronger bonds at the expense of weaker ones.

In other cases the number of bonds broken or formed can be important. Since all the bonds are similar in strength, making more bonds than are broken means the release of energy.

In mathematical terms. In summary, there are two factors which determine whether a gaseous reaction will be exothermic or not: 1 the relative strengths of the bonds as measured by the bond enthalpies, and 2 the relative number of bonds broken and formed.

In other words, breaking a bond is an endothermic process, while the formation of bonds is exothermic. Bond enthalpy, also known as bond dissociation energy, is defined as the standard enthalpy change when a bond is cleaved by homolysis, with reactants and products of the homolysis reaction at 0 K absolute zero. For instance, the bond enthalpy, or bond-dissociation energy, for one of the C-H bonds in ethane C 2 H 6 is defined by the process:.

The strength of bonds between different atoms varies across the periodic table and is well documented. Each bond in a molecule has its own bond dissociation energy, so a molecule with four bonds will require more energy to break the bonds than a molecule with one bond.