Chemical and Nuclear Potential Energy

A tank of gasoline and a pellet of uranium fuel both sit inert in a storage room. Neither is moving, glowing, or releasing energy. Yet the gasoline stores about 44 MJ/kg of chemical potential energy, and the uranium stores about 82,000,000 MJ/kg of nuclear potential energy: roughly 1.9 million times more per kilogram. The energy is there, locked in the arrangement of particles, waiting for a trigger.

Chemical potential energy is stored in the arrangement of electrons around atoms. When those arrangements change (a chemical reaction), energy is released or absorbed. A match provides the activation energy to trigger coal's combustion; once started, the reaction sustains itself. Nuclear potential energy is stored in the arrangement of protons and neutrons in the nucleus. When those arrangements change (fission or fusion), far more energy is released per unit mass because the strong nuclear force holding nuclei together is vastly stronger than the electromagnetic forces holding electrons in orbit.

Both are forms of potential energy: energy stored by virtue of configuration, not motion. Gravitational PE is stored in an object's position above the ground. Chemical PE is stored in molecular bonds. Nuclear PE is stored in nuclear binding. The common thread is that energy was invested to create the configuration, and it can be recovered when the configuration changes.

Worked Example

A natural gas molecule (CH₄) stores about 890 kJ/mol of chemical PE. A U-235 atom stores about 200 MeV of nuclear PE (released upon fission).

• Convert units. 200 MeV = 3.2 x 10⁻¹¹ J per atom. One mole of U-235 = 6.02 x 10²³ atoms.
• Per-mole nuclear energy. 3.2 x 10⁻¹¹ x 6.02 x 10²³ = 1.93 x 10¹³ J/mol = 1.93 x 10¹⁰ kJ/mol.

How many times more energy per mole does U-235 fission release compared to methane combustion?

1.93 x 10¹⁰ / 890 = about 22 million times more per mole. This ratio (millions to one) is fundamental to nuclear energy's density advantage.

Every power plant, chemical or nuclear, is running the same trade: rearrange particles and collect what escapes. The only difference is how tightly those particles were bound to begin with, and that single variable spans a million-fold range in what a kilogram of fuel can deliver.

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