Chemical energy, typically food or fuel, resides in the bonds between molecules, while mechanical energy provides the ability to work resulting from position or movement. Chemical energy converts to mechanical energy when reactions release heat allowing one object to apply force to a second, transferring the ability to perform work.
Chemical energy exists as potential. When the molecules that it inhabits metabolize, chemical energy is released into a kinetic state. In some instances, that release is explosive, causing the rapid conversion of chemical energy to thermal and radiant energy.
Plant cells convert radiant energy to chemical energy using photosynthesis, ultimately manufacturing carbohydrates. Carbohydrates are stockpiled until biochemical processing breaks down the complex compounds into simpler elements, releasing thermal energy. Machines convert fuel by burning to produce force that impacts an object. An example is the generation of steam that expands against an object, overcoming its resistance and allowing it to move.
Mechanical energy is either potential, based on its position, or kinetic as it gives an object the ability to perform work. A wrecking ball at the apogee of its swing exhibits potential energy. The moment the ball hits a building, it becomes kinetic, transferring the capacity to move to the wall and forcing it to crumble.