chemical potential energy

Meaning: Chemical potential energy is the potential energy a substance holds because of the electrostatic attractions and repulsions among its electrons and nuclei. Fuels, food and batteries are common stores. In a reaction it can be converted into the kinetic energy of particles (thermal energy), light, electrical work or mechanical work. If the products sit at lower potential energy than the reactants (more stable bonds), energy goes out to the surroundings. If the products sit higher, energy must be taken in.

On the MCAT: Passages ask you to trace energy conversions: chemical to thermal in combustion, chemical to electrical in a galvanic cell, chemical to mechanical in muscle contraction. Apply conservation of energy: a drop in chemical potential energy appears as an equal gain in other forms (heat, work, light) in the system and its surroundings. You may also read an energy diagram, where reactants higher than products means energy is released (exothermic).

Common confusion: Students say energy is released when bonds break. Breaking a bond requires energy input; energy is released when new bonds form, and the net result depends on which is larger. The same reasoning applies to ATP: the energy comes from the hydrolysis products being more stable overall, not from the bond simply "snapping."