Let's consider a concrete example- a pendulum. The energy of the pendulum comes in two forms:
|Energy =||kinetic energy||+||potential energy|
You can write a total energy expression of this sort for a chemical reaction, like the combustion of hydrogen. The chemical energy has a kinetic component (the motion of electrons and nuclei within the molecules) and a potential component (the attraction of the electrons for the nuclei, along with repulsions between electrons and repulsions between nuclei). The molecules are also moving, which gives them kinetic energy overall. If you decrease the potential energy of the reaction mixture (by jumbling the nuclei and electrons around to maximize attractions and minimize repulsions), you must increase the kinetic energy of the mix. That increased kinetic energy appears as heat.
A mousetrap is a metaphor for this sort of conversion of energy. Before the trap is sprung, the energy is all potential energy, "stored" in the spring. When the trap is sprung, the spring can stretch, and the bar slams down - potential energy becomes kinetic energy. Chemical bonds are similar to the spring. When the bond is snapped, the potential energy becomes kinetic. The repulsion between the nuclei of the freed atoms is no longer balanced by the attraction they have for the bonding electrons, and they fly away from each other.
Author: Fred Senese firstname.lastname@example.org
Copyright © 1997-2010 by Fred Senese
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Last Revised 08/17/15.URL: http://antoine.frostburg.edu/chem/senese/101/thermo/faq/print-how-energy-transforms.shtml