Eli5: why do acid base reactions generate heat?


follow-up: what determines whether or not a reaction generates heat?

In: Chemistry

A reaction that releases heat is called exothermic, and it depends on the energies involved. Energy needs to be conserved. If the chemical binding energy of the products is less than that of the reagents then that extra energy is released as heat.

All chemical reactions involve energy.

1. It **takes energy** to break bonds.
2. Energy **is released** when bonds are formed.

Chemical reactions that release energy are called exothermic. In exothermic reactions, more energy is released when the bonds are formed in the products than is used to break the bonds in the reactants.

The **Law of Conservation of Energy** states that “energy cannot be created or destroyed in a chemical reaction, it can only be transformed from one form to another”. Thus, the excess energy produced is released in the form of heat.

An acid-base reaction is one such exothermic reactions, and thus releases energy in the form of heat

You have an acid which is a solution with extra protons in it. A proton is a hydrogen atom that lost its electron. They call it a H^(+) ion. This ion will bond to a water to make a H3O^(+) Hydronium ion. These ions are have a lot of energy. You can make a battery with the solution.

On the other side of the acid/base spectrum, we are stealing a H^(+) from a water to make a OH^(-) ion. This is a hydroxide ion. These ions also have a lot of energy.

So you mix them together you get salt and water which are really stable, so the extra energy has to go somewhere so it gets released as heat.