Chemical energy is defined as the form of potential energy stored within atoms and molecules. Usually, it’s the energy stored within chemical bonds, but it’s also the energy of the electron arrangement of ions and atoms. Chemical energy is observed when a chemical reaction occurs or matter changes forms. Energy is either absorbed or released when chemical energy changes form as the result of a chemical change.
Key Points: Chemical Energy
- Chemical energy is a form of potential energy found within chemical bonds, atoms, and subatomic particles.
- Chemical energy can be observed and measured only when a chemical reaction occurs.
- Any matter that is a fuel contains chemical energy.
- The energy can be released or absorbed. For example, combustion releases more energy than is needed to initiate the reaction. Photosynthesis absorbs more energy than it releases.
Chemical Energy Examples
Fuels are a familiar form of chemical energy. While combustion is an example of the release of chemical energy, there are several other examples:
- Coal: The combustion reaction converts chemical energy into light and heat.
- Wood: Combustion converts chemical energy into light and heat.
- Petroleum: Petroleum may be burned to release light and heat or changed into another form of chemical energy, such as gasoline.
- Chemical batteries: Batteries store chemical energy to be changed into electricity.
- Biomass: Combustion of biomass converts chemical energy into light and heat.
- Natural gas: Combustion converts chemical energy into light and heat.
- Food: Digestion converts chemical energy into other forms of energy used by cells.
- Air bags: Air bags contain the compound sodium azide, which is ignited when the bag is activated. The reaction produces nitrogen gas, which fills the air bag, converting chemical energy into kinetic energy.
- Cold packs: Chemical energy is absorbed in a reaction.
- Propane: Burning propane yields heat and light.
- Gasoline: Gasoline is a type of chemical energy that is burned to run automobiles. Chemical energy is eventually converted into kinetic energy.
- Hot packs: Chemical reaction produces heat or thermal energy.
- Matches: Striking a match converts the chemicals on the match head into other compounds, releasing light and heat.
- Photosynthesis: Photosynthesis transforms light (solar energy) into chemical energy (the sugar glucose).
- Cellular respiration: Cellular respiration is a set of reactions that changes the chemical energy in glucose into chemical energy in ATP, a form our bodies can use.
How Chemical Energy Works
For the most part, chemical energy is energy stored within chemical bonds. In a chemical reaction, chemical bonds are broken and new ones are formed, changing products into reactants. When breaking bonds releases more chemical energy than forming new bonds absorbs, then the reaction is exothermic and heat is released. But, sometimes it takes more energy to form chemical bonds to make products than breaking bonds in reactants releases. This type of chemical reaction absorbs heat or other energy and is endothermic. Both exothermic and endothermic reactions involve chemical energy because energy is converted into other forms by a chemical reaction.
References
- Christian, Jerry D. (1973). “Strength of chemical bonds”. Journal of Chemical Education. 50 (3): 176. doi:10.1021/ed050p176
- Jain, Mahesh C. (2009). “Fundamental Forces and Laws: A Brief Review”. Textbook of Engineering Physics, Part 1. PHI Learning Pvt. Ltd. ISBN 978-81-203-3862-3.
- McCall, Robert P. (2010). “Energy, Work and Metabolism”. Physics of the Human Body. JHU Press. ISBN 978-0-8018-9455-8.
- Schmidt-Rohr, K. (2015). “Why Combustions Are Always Exothermic, Yielding About 418 kJ per Mole of O2“. J. Chem. Educ. 92: 2094–2099. doi:10.1021/acs.jchemed.5b00333