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Unit 12: Alternative Energy Page 27 of 31

This is why the bag containing the dehydrated magnesium sulfate is

unheated Epsom salt became cold dissolved in water.
when you added water. Repeat this experiment using table
On the other hand, when salt. Do you observe a temperature
dehydrated Epsom salt dissolves in change when the table salt

water, more energy is given off by dissolves in water?
the ions becoming surrounded by
water molecules than is needed to
break the magnesium and sulfate
ions from the crystals. This is why
the bag containing the dehydrated
Epsom salt became warm when
you added water.

Most instant hot packs and cold
packs that are available in
drugstores work on the principle
just discussed. When the cold or
hot pack is needed, the bag is

squeezed to cause the water and
salt to mix. Depending on the salt
used in the pack, energy is either
absorbed (cold pack) or given off
(hot pack). Ammonium nitrate is
the most commonly used salt in
cold packs. And calcium chloride is
the most commonly used salt in
hot packs.

Other Things to Try

Repeat this experiment using a
thermometer to measure the
temperature change when the
Epsom salt is dissolved in water.
Use the thermometer to measure
the temperature change when

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