How is chemical energy in fuel transformed into heat?

Chemical energy is a type of stored potential energy contained in the specific structural arrangement of atoms or molecules. This arrangement is primarily the result of chemical bonds within a molecule. Chemical energy of a chemical substance can be transformed to other forms of energy by specific chemical reactions.

For example, when a fuel is burned, the chemical energy is converted to heat energy. The majority of this type of energy is lost to the external environment.

Green plants transform solar energy into chemical energy through the process known as photosynthesis. Other forms of energy such as electrical energy can be converted to chemical energy through electrochemical reactions.

When digested food is metabolized within in a biological organism, chemical energy is also converted into heat energy.

Humans consume plants and/or humans eat animals which earlier had consumed plants. The stored chemical energy within the plant or animal cells is transferred into the cells of the human being's body. Most, if not all, of the human system processes such as digestion of food, the circulatory system, respiration, the immune system, etc., rely upon cells which are able to convert the stored chemical energy into work and heat in a process known as cellular respiration.

Chemical energy is stored in foods we consume along with fuels we use and can be released when these types of molecules undergo chemical reactions. One of the most commonly used equations utilized by biologists, refers to how energy is released from glucose during the process of cellular respiration, as shown below:

A chemical reaction refers to a series of chemical changes that result in the production of one or more new chemical substances. These types of chemical changes are always accompanied by a change in the overall energy of the system. This refers to the idea that energy is either given off or released during a specific reaction, or energy is taken in or consumed during a specific reaction.

Endothermic reactions refer to specific reactions which utilize or take in energy in order for the reaction to take place. These types of reactions contain products that have more potential chemical energy than the reactants.

When an athlete sustains a muscle injury during a basketball game, the team doctor will place a cold pack on the general location of the injury. In order to 'activate' the cold pack, a seal is broken that separates two containers with the plastic bag. As the contents from the separate containers begin to react, energy is absorbed from the surrounding environment. As the doctor places the cold pack on the injured location of the athlete, the athlete's body will begin to supply some of the energy that is required to get the reaction going. What the athlete experiences as "cold" has to do with the temperature of that area of the athlete's body changing as heat flows from the body to the cold-pack.

The Flying Turtle teachers' resource site contains a lively set of information about energy changes.

TEACHER REOURCES ALERT!

For more information on student misconceptions and classroom activities on chemical energy reactions, please visit this ScienceNetLinks website.

Exothermic reactions refer to specific reactions which release or liberate energy.
These types of reactions contain products, which have an overall decreased level of potential energy than the reactants, since energy was primarily released in the form of heat. The water and the carbon dioxide in the example below carry less potential energy than the propane and oxygen.
When you are standing next to a barbecue grill, you feel the heat being released by the combustion reaction that is taking place around the burners. The reaction of the propane gas found in barbecue grills is described below: