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chemical energy

n. (context chemistry English) The net potential energy liberated or absorbed during the course of a chemical reaction

chemical energy

n. that part of the energy in a substance that can be released by a chemical reaction

Chemical energy

In chemistry, chemical energy is the potential of a chemical substance to undergo a transformation through a chemical reaction to transform other chemical substances. Examples include batteries, food, gasoline, and more. Breaking or making of chemical bonds involves energy, which may be either absorbed or evolved from a chemical system.

Energy that can be released (or absorbed) because of a reaction between a set of chemical substances is equal to the difference between the energy content of the products and the reactants, if the initial and final temperatures are the same. This change in energy can be estimated from the bond energies of the various chemical bonds in the reactants and products. It can also be calculated from ΔU, the internal energy of formation of the reactant molecules, and ΔU the internal energy of formation of the product molecules. The internal energy change of a chemical process is equal to the heat exchanged if it is measured under conditions of constant volume and equal initial and final temperature, as in an open container such as a bomb calorimeter. However, under conditions of constant pressure, as in reactions in vessels open to the atmosphere, the measured heat change is not always equal to the internal energy change, because pressure-volume work also releases or absorbs energy. (The heat change at constant pressure is called the enthalpy change; in this case the enthalpy of reaction, if initial and final temperatures are equal).

Another useful term is the heat of combustion, which is the energy mostly of the weak double bonds of molecular oxygen released due to a combustion reaction and often applied in the study of fuels. Food is similar to hydrocarbon and carbohydrate fuels, and when it is oxidized to carbon dioxide and water, the energy released is analogous to the heat of combustion (though not assessed in the same way as a hydrocarbon fuel — see food energy).

Chemical potential energy is a form of potential energy related to the structural arrangement of atoms or molecules. This arrangement may be the result of chemical bonds within a molecule or otherwise. Chemical energy of a chemical substance can be transformed to other forms of energy by a chemical reaction. As an example, when a fuel is burned the chemical energy of molecular oxygen is converted to heat, and the same is the case with digestion of food metabolized in a biological organism. Green plants transform solar energy to chemical energy (mostly of oxygen) through the process known as photosynthesis, and electrical energy can be converted to chemical energy and vice versa through electrochemical reactions.

The similar term chemical potential is used to indicate the potential of a substance to undergo a change of configuration, be it in the form of a chemical reaction, spatial transport, particle exchange with a reservoir, etc. It is not a form of potential energy itself, but is more closely related to free energy. The confusion in terminology arises from the fact that in other areas of physics not dominated by entropy, all potential energy is available to do useful work and drives the system to spontaneously undergo changes of configuration, and thus there is no distinction between "free" and "non-free" potential energy (hence the one word "potential"). However, in systems of large entropy such as chemical systems, the total amount of energy present (and conserved by the first law of thermodynamics) of which this Chemical Potential Energy is a part, is separated from the amount of that energy— Thermodynamic Free Energy (which Chemical potential is derived from)—which (appears to) drive the system forward spontaneously as its entropy increases (in accordance with the second law).

Usage examples of "chemical energy".

Now it is obvious that warmth, light and chemical energy, though they all play an essential part in living organisms, could never by themselves bring about that 'catching from chaos, carbon, water, lime and what not and fastening them into a given form' which Ruskin describes as the activity of the spirit in the plant.

Europan life would have to be powered by chemical energy, as it is around Earth's underwater volcanic vents.

I didn't realize the human body contained quite so much chemical energy.

The addition of diesel fuel was partly to provide an additional element of chemical energy, but mainly to act as a wetting agent, the better for the internal shock wave to propagate within the explosive mass and hasten the detonation.

In such a state it was at the mercy of nocturnal organosilicate predators and scavengers, who instead of the sun relied on a round-the-clock production of chemical energy.

Instead of con-verting sunlight into chemical energy, as plants do, it converts light directly into electricity.

It's about the same as the chemical energy in a tank of automobile gas.

For, even though it might have originated on a planet that was so tiny that chemical energy-although that was hard to visualizewould be sufficient to lift it out of the pull of gravity, to travel the distance that stretched between the stars only one thing would suffice.

The structures also operate at a higher temperature than the ambient seabed, and they use chemical energy to make that possible.

It is thus a perfectly reversable action, requiring only the electro-chemical energy from the photo-cells.

Soon humans would dig out fossil fuels, burning up the chemical energy stored in forests and bogs over millions of sunbathed years, then they would meddle with the hearts of atoms, then they would tap the energy of the vacuum, and so on.