We can use the spring analogy below to illustrate why combustions
in strongly electronegative media are exothermic, or heat-emitting.
Let the ball in the middle symbolize the electrons, drawn
either toward oxygen at the left, or carbon and hydrogen at
the right. The stronger spring to the left represents the
greater electronegativity of oxygen, and the weak spring at
the right, the lesser electronegativities of carbon and hydrogen.
If water and CO2
were to react to form methane and O2,
electrons would be moved away from oxygen, against oxygen's
natural electronegativity. This corresponds to using energy
to push the ball to the right, thereby stretching the strong
spring. This energy is stored in the spring (or in the methane
molecules) as potential, or latent, energy.