Chemical Energy is released when bonds form in a chemical reaction, often producing heat as a by-product (exothermic reaction).
There are two important terms to know in the study of chemical energy.
1. Exoergic: An exothermic (exoergic) nuclear reaction is a reaction that releases energy when chemical bonds form.
2. Endoergic: an endothermic (or endoergic) reaction is one that requires an input of energy to take place. Note that energy is often needed to break up bonds before forming new bonds. Example: during photosynthesis, energy from the sun is needed/used to break the CO2 and H2O bonds. Glucose is produced and an O2 bond is formed as a result.
Batteries, biomass, petroleum, natural gas, and coal are examples of stored chemical energy. Usually, once chemical energy is released from a substance, that substance is transformed into an entirely new substance.
For example, when an explosive goes off, the chemical energy stored in it is transferred to the surroundings as thermal energy, sound energy, and kinetic energy.
Let's see one good example in the fire-place illustration below.
Dry wood is a store of chemical energy. When a fire is applied to wood, the molecules in the wood fragments react with the oxygen (air). This reaction results in new chemical bonds of carbon dioxide, carbon monoxide, and water.
As it burns in the fireplace, chemical energy is released and converted to thermal energy (heat) and light energy. Notice that the wood now turns into ashes (a new substance)
Food is also a good example of stored chemical energy. This energy is released during digestion. Molecules in our food are broken down into smaller pieces. As the bonds between these atoms loosen or break, a chemical reaction will occur, and new compounds are created. When the bonds break or loosen, oxidation occurs almost instantly.
In the example above, notice that new compounds are formed from the breakdown of other molecules or atoms. A chemical reaction causes that.
A chemical reaction is involved in this breakdown. The energy produced keeps us warm, maintain and repair bodies, and makes us able to move about. Different foods store different amounts of energy. The energy in food is measured in kilocalories (or Calories). Can you think of some very good examples of chemical energy?
Click to see an example of how chemical energy is released from coal to produce electricity.