Fusion
Definition and meaning of Fusion in chemistry.
Fusion is the phase change in which a solid absorbs heat and becomes a liquid at its melting point, with the temperature remaining constant throughout the transition.
In more detail
During fusion, absorbed energy goes into overcoming the intermolecular attractions or lattice forces holding particles in fixed positions, rather than increasing their average kinetic energy, so the solid and liquid coexist at a single, constant melting temperature until the phase change is complete. The amount of heat required to melt one mole of a substance at its melting point is called the molar enthalpy (or heat) of fusion, ΔH_fus, a characteristic thermodynamic property. Fusion is the exact reverse of freezing (solidification), and for a pure substance both occur at the same temperature, differing only in the direction of heat flow.
Key facts
| Also called | Melting (solid → liquid transition) |
|---|---|
| Reverse process | Freezing (solidification) |
| Key quantity | Molar enthalpy of fusion, ΔH_fus |
| Field | Physical Chemistry |
Melting 1 mole of ice at 0°C to liquid water at 0°C requires 6.01 kJ of heat, the molar enthalpy of fusion of water.
Frequently asked questions
Is chemical fusion the same as nuclear fusion?
No. In chemistry, fusion refers to melting, a physical phase change of a substance. Nuclear fusion is an entirely different process in which atomic nuclei combine to form a heavier nucleus, releasing energy (as in the sun or a hydrogen bomb).
Why doesn't temperature rise while a solid is melting?
All the heat absorbed during fusion is used to break the ordered arrangement of particles in the solid lattice; only after melting is complete does further heating raise the liquid's temperature.