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# Heat of Solution

## Amount of heat absorbed or released in the formation of a solution

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Dealing with Aches and Pains

### Dealing with Aches and Pains

Credit: 316th ESC
Source: http://www.flickr.com/photos/66549145@N08/7584568630

Exercising can put strains on the muscles.  In addition, sore muscles can come from hard work or as a result of an accident.  Tissues damage and inflammation can be reduced by using heat or cold packs.

#### News You Can Use

• When a crystalline solid dissolved in water, there is usually a noticeable temperature change.  For some materials, the temperature will decrease, while for other compounds the temperature will increase.  This change in temperature is called the heat of solution. Instant ice packs take advantage of this phenomenon – when water and the compound are mixed, the temperature drops and the pack can be used for cooling.
• Ice packs come in all shapes and sizes. This allows them to be used for different parts of the body.
• Credit: US CPSC
Source: http://www.flickr.com/photos/uscpsc/7349054524/

Ice pack sizes [Figure2]

• Some compounds can form supersaturated solutions.  If a saturated solution is prepared at a high temperature and carefully cooled, the material will remain in solution at a lower temperature.  When precipitation is initiated, the compound forms crystals and precipitates from solution, releasing heat in the process.
• Heat packs employ this principle for providing heat to sore muscles.  After use, the pack can be placed in boiling water to redissolve the entire solid so the pack can be used again.
• In this video, you can see the transition from a supersaturated solution to a saturated one: http://www.youtube.com/watch?v=XSGvy2FPfCw

#### Show What You Know

1. What is the hydration enthalpy of an ion?
2. Explain how a sodium acetate heat pack works.
3. How does an instant ice pack work?
4. When should ice or heat be used with sore muscles?

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