Sodium acetate heat pads has video

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Sodium Acetate Heat Pads  (has video)   C H 3 C O O Na +
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Sodium acetate trihydrate has a freezing point (or melting point) of  58  ° C – a temperature similar to that of hot water from a tap. Sodium acetate trihydrate also has the interesting property that it  can  be  supercooled  –  cooled  below  its  freezing  point  without  actually freezing.  This is the basis of sodium acetate heating pads: A supercooled solution of sodium acetate in water is sealed inside a  plastic bag containing a metal disk. The  metal  disk  can  be  pressed  to  release  a  tiny  crystal  of  sodium  acetate which instantly provides a “nucleation site” so that the rest of  the solution solidifies into a lattice. Heat is released as the cations and anions come together to form an  ordered ionic lattice (enthalpy of lattice formation!), warming the heat  pad up to about 58  ° C. The  heat  pad  can  be  “regenerated”  by  heating  it  enough  that  the  sodium acetate trihydrate melts then allowing it to slowly cool (without  pressing the disk) without freezing. Sodium Acetate Heat Pads  (has video)   C H 3 C O O Na +
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  • Fall '06
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