What Is Chemical Energy?

Lucy Bell-Young

by Lucy Bell-Young

16th September 2020

Chemical energy is what allows our bodies to keep functioning. In more basic terms, we, along with every living thing on this planet, need chemical energy to survive. Because it’s most commonly found in food, chemical energy is stored in the atoms, electrons, and molecular bonds that make up our bodies. From here, it undergoes several processes and chemical reactions in order to release energy to us. 

But this isn’t the only example, nor use, of chemical energy. It can also be found outside our bodies, and is used in a variety of different ways. This article explains where you can find chemical energy, how you can measure it, how it’s released, and what it’s used for.

Where Can You Find Chemical Energy?

  1. Inside the atom

Chemical energy is stored in the bonds that make up chemical compounds. This means that chemical energy is commonly contained within the atoms and molecules inside every living organism. When stored in this way, energy can be classified into two categories: nuclear energy and chemical energy.

Nuclear energy is released when nuclei are either split, or fused in the forms of electromagnetic radiation, including gamma rays, heat, and subatomic particles. These aren’t examples of chemical energy as they’re generated through nuclear decay or nuclear reactions. Chemical energy is released when molecular bonds break, or when they form during a usually exothermic reaction. 

Another difference is that while our bodies, and indeed all living organisms, need chemical energy to survive, we make no use of the nuclear energy or nuclear processes taking place inside our atomic nuclei.  

3D Illustration of an atom, which contains chemical energy

Chemical energy is contained inside the atoms and molecules of every living thing

  1. Energy levels and electrons

We touched on it briefly, but chemical reactions that release energy are typically exothermic, i.e. they release heat. These reactions can also release energy in the form of light, and even sound. This process involves the movements of electrons from lower energy levels to higher energy levels, then back again. 

The amount of chemical energy released in these contexts is directly proportional to the speed of the reaction. Reactivity is correlated with how the electrons are arranged on different energy levels or shells.

For instance, when oxygen reacts with hydrogen, it’s fast and explosive, and tremendous amounts of heat, light, and sound energy are released almost instantly. By comparison, when oxygen reacts with iron, which is also known as rusting, the process is slow and barely noticeable. In this example, energy is released over a longer period of time.

  1. Molecular bonds

Chemical energy is basically stored energy in molecular bonds. It can either be abruptly released, such as when oxygen reacts with hydrogen, or it can be gradually and methodically released, such as in metabolic processes in the body. 

The latter explains why chemical energy is also found in food, specifically within its molecular bonds. The organic constituents of organisms, such as the proteins in the muscles and the glucose, or fructose in fruits, are sources of chemical energy.

How Is Chemical Energy Measured?

Before we can understand how chemical energy is measured, we first need to define energy. The simplest and classic definition of energy in physics is ‘the capacity to do work.’ This means that a certain amount of energy need to be transferred or converted in order to accomplish something.

  1. The basic formula for energy

‘Work’ is defined as the product of force and distance. This implies motion and mass, since force is simply the product of mass and acceleration. Therefore, work is just an application of energy. For example, the chemical energy of a battery can be used to move mass or accelerate mass across distances through the use of a motor.

This is the basis for the mechanical measurement of chemical energy. The basic formula for energy is one half the mass multiplied by the square of the velocity. It can also be expressed in terms of power multiplied by time, such as kilowatt-hour.

The basic mechanical formula for energy has many derivations, but it all boils down to the motion of mass. For example, the heat of boiling water is actually particles of water moving rapidly because of high amounts of energy. The same is true for any hot object – as another example, radiation energy is simply the product of the motions of excited particles.

  1. Units of measurements

With all this in mind, the standard metric system or SI unit of measure for energy is joules (J). This is equivalent to one Newton of force acting through one metre distance, and it can be converted into other measurements of energy, like calories.

One calorie is the amount of energy needed to raise one gram of water by 1°C. This makes one calorie the equivalent to 4.184 J. Similarly, a BTU, or British Thermal Unit, is the unit of energy required to raise the temperature of one pound of water by 1°F.

Most chemical reactions are exothermic and give off heat. However, endothermic chemical reactions still involve energy. In this context, instead of releasing energy, one of the reactants absorbs energy. The temperature differential in an endothermic reaction is still measurable using the standard formula and unit of measurements used to calculate the energy released from exothermic reactions.

Exothermic and endothermic reaction

How To Calculate Chemical Energy

As previously mentioned, chemical reactions can either release (exothermic) or absorb (endothermic) energy. During a chemical reaction, the molecular bonds of the constituent elements or chemical groups in compounds are broken, and new bonds are formed.

Calculating the chemical energy in a reaction simply involves subtracting the energy of the products from the energy of the reactants. The difference is either released or absorbed as heat. If the energy of the products is greater than the energy of the reactants, heat is absorbed. If the energy of the products is lesser than the energy of the reactants, heat is released.

Theoretically, the type of reaction can actually be predicted, whether endothermic or exothermic. However, the precise amount of energy must still be experimentally determined.

How Is Chemical Energy Released?

The chemical energy produced during a reaction is released in several ways, depending on the reactants involved. While it can be produced as light, chemical energy is usually released in the form of heat.

In the body, the main way chemical energy is released is through metabolic processes, specifically catabolism. This allows cells to release stored energy by breaking down the molecular bonds in food. In this context, the reaction is exothermic, and the chemical energy is released to allow the body to function.

Outside of the body, chemical energy is released in a similar way: a chemical reaction causes the bonds in compounds to break, releasing energy. In the same way that the body converts it into mechanical energy (which basically allows us to move and operate), chemical energy can be converted into many forms of energy, depending on where it’s released from. For example, when contained in coal, chemical energy can be converted into electrical energy.

Aerial view of oil refinery plant from industry zone

Chemical energy isn’t only used to power our bodies, it’s also used to power industries

What Do We Use Chemical Energy For?

Chemical energy has many uses. Predominantly, it’s used by almost all life-supporting functions, from respiration and metabolism to photosynthesis. To put it simply, every living thing needs chemical energy in order to survive, whether this is consumed from organic food or inorganic compounds.

But chemical energy isn’t just used inside the body. In fact, humanity’s largest use of energy to date is fossil fuel, which is used to power industries, transportation, and electricity. Batteries are another common source of chemical energy, and they convert this into electrical energy that is then stored away for later use.

Is Fire Chemical Energy?

Fire is the result of a rapid reaction between oxygen and combustible materials, like wood. In the process, heat and light energy are released as molecular bonds are broken and new ones are formed. Therefore, fire is basically a form of chemical energy because of the reactions taking place.


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