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A saturated solution contains the maximum amount of solute that a solvent can hold. Supersaturated solutions can be prepared by heating a solution. By adding heat to the solution, the solvent gains kinetic energy and can dissolve and accommodate more of the solute. Some supersaturated solutions, such as sodium acetate, when allowed to slowly cool will remain solutions. In this case the solutions are thermodynamically unstable because the solvent contains more solute than theoretically possible. If the solution is disturbed (by adding a seed crystal, scratching the container, or by vibrations (such as sound), the solute precipitates out of solution. With supersaturated sodium acetate, this happens very quickly. Sodium acetate crystallizes and entraps water molecules within the crystal lattice. The process is exothermic and the heat is often referred to as the enthalpy of crystallization. The process can be repeated by simply reheating the solution until all of the sodium acetate dissolves. Companies have made use of this by selling "hot hands" for hiking and skiing.