Chemical EnergyTable of contents
Chemical energy is a concept that is unmistakably related to every single process of life on earth. Simply put, chemical energy is the potential of a chemical system to undergo a transformation from one system to another; or to impart a transformation on another chemical system. Through simple redox chemistry, energy can be harvested from nearly every molecule on earth. Chemical energy powers the cars that we drive, fuels our bodies, creates glucose, and all living creatures on the planet.
IntroductionChemical reactions undoubtedly involve the making and breaking of chemical bonds (ionic and covalent) and the chemical energy of a system is the energy released or absorbed due to the making and breaking of these bonds. If a bond is broken, energy is released; and if a bond is formed, energy must have been absorbed. As these occur, a change in the chemical energy of the system also occurs. Within each bond of a molecule is an experimentally determined amount of energy, that upon the breaking of that bond is released into the chemical system. The energy within these bonds are 'stored' and can be easily thought of as potential energy. Upon the breaking of these bonds the energy is released thereby creating usable energy. In terms of amount of energy, those more favorable to form require less energy input than the bonds that are more difficult to form. The result is higher and more accessible potential energy in less favorable bonds when compared to more favorable. Chemical energy coincides closely with the other forms of energy in a system including both thermal and nuclear energy. All of these sources are additive, resulting in the total energy of the system (Usystem). With this said, we must keep in mind the basics of internal energy of any system: HTTP Status: BadRequest(400) (click for details)
As is true with any chemical system, energy must be defined as both the potential and kinetic energies due to the fact that atoms are subject to both repulsion and attraction to one another as well as being with all molecules of the system as a whole. To describe the concept of chemical energy further, we can use the simple reaction: HTTP Status: BadRequest(400) (click for details)
Figure 1: A simple energy level diagram depicting energy must be absorbed by the chemical system in the formation of bonds and is therefore released if and when the bond is broken. This energy may also be transferred when presented with a suitable molecule capable of absorbing the excess energy. Chemical energy can be seen in our every day lives more than most of us would ever even believe and is essential to fuel every living creature day in and day out. Chemical energy is responsible for powering the cars that we drive, providing heat to our homes, cooking our food (propane grills), and creating usable energy in every living animal cell on earth. Formation of ATP: HTTP Status: BadRequest(400) (click for details)
Although this appears to be a reasonably complex chemical equation, the concept is one that most are quite familiar with by now. It is in fact two redox reactions occurring in unison. As the molecules of glucose are broken into subsequent parts, energy is released (1mole=686kcal or 2870kJ), cellular machinery uses this energy to form phosphate bonds on the adenosine diphosphate molecule (ADP) and form the higher, more usable energy containing adenosine triphosphate molecule and waste products. We do not need to consider the role of oxygen in this explanation, as it simply acts as an electron acceptor for the excess carbon atom. As you can see, this process has the potential to function in a cyclic fashion. As molecules of ATP are produced, cellular metabolism breaks these molecules apart to use the energy contained within the strong phosphate bonds and results in ADP + Energy. What this process provides is usable, effective, and long term energy storage. The combustion of fuel in cars: HTTP Status: BadRequest(400) (click for details)
The hydrocarbon methane (CH4) as we know, is the main component of the gasoline rely so heavily upon. That when combined with an oxidizing agent O2 (g), and ignited, reacts violently in a subsequent chain reaction and nearly complete combustion. The result is the release of a significant amount of energy with of course water vapor and the ever controversial CO2 as waste products. Each bond of hydrogen broken releases around 410kJ of energy resulting in a net release of about 1640kJ per molecule of methane. This however, when combined with all molecules in the reaction leads to a total net of 810kJ per mole. As reactants are formed into products energy must be put into the system that is significant enough to break the bonds of the CH4 molecule (the endothermic step); and as the bonds are reformed during the creation of the product, an even greater amount of energy is released, that had been previously contained within those bonds.
As you can see, chemical energy plays a crucial role into each and every one of our every day lives. Through simple reactions and redox chemistry, the breaking and forming of bonds, energy can be extracted and harnessed into a usable fashion. References
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