Instant ice pack

To provide cold therapy for cuts, bruises, sprains, and lacerations, an instant ice pack for first-aid treatment uses a chemical reaction that requires heat in order to occur. An instant Ice-Pack contains two compartments — one containing liquid water, the other a solid. The pack is activated by squeezing the liquid compartment to break an inner seal that permits the mixing of the two compartments. Heat is withdrawn from the surroundings by the reacting chemicals, lowering the temperature of the ice-pack contents. 

Question 10.5 What Causes an Instant Ice-Pack to Cool ... 

An instant ice pack for first-aid treatment uses the endothermic nature of the dissolution of an ionic salt in water to provide cold therapy. Two typical materials that absorb heat as they dissolve in water are ammonium nitrate and ammonium chloride ... 

For example., suppose a sample instant ice pack contains 75.0 mL of water and 25.0 g of NH4NO3. We will assume that all 25.0 g of NH4NO3 dissolves in the liquid water (Remember that NH4 salts are soluble, although the solubility may be limited with the small volume of water present ) ... 

Assuming that we start at 298 K, the final T will be around 270 K or —3°C or 25°F. Brrr Our calculation has also involved a number of other assumptions, including that we have assumed a temperature-independent enthalpy of reaction and a temperature-independent heat capacity for the water. We have also assumed that the water does not freeze (would release some heat). Nevertheless, the calculation gives a fairly reasonable estimate of the temperature drop that provides the cooling therapy of an instant ice pack. 

C) Commercial instant ice packs are available that contain a mixture of ammonium nitrate and water separated by a barrier. When the ice pack is twisted, the barrier breaks and the two substances mix. The temperature rapidly decreases as the ammonium nitrate dissolves in the water. Describe the changes in enthalpy, entropy, and free energy during this process. 

Instant ice packs are used to cool food and also to numb sports injuries on the field of play. The ice packs do not require refrigeration and can be activated simply by striking them with a fist. 

Athletic trainers use instant ice packs that can be cooled quickly on demand. Squeezing the pack breaks an inner container, allowing two components to mix and react. This reaction makes the pack become cold. Describe the heat flow for this spontaneous process. 

A Figure 13.5 An instant ice pack, containing ammonium nitrate, used to treat athletic injuries. To activate the pack, the container is kneaded, breaking the seal separating solid NH4NO3 from water. The heat of solution of NH4NO3 is positive, so the temperature of the solution decreases. 

Ammonium nitrate (NH4NO3) dissolves in water with an endothermic heat of reaction of 26.4 kJ mol. How much ambient heat will be absorbed when 2.0 kg of ammonium nitrate dissolves in water (This reaction is utilized in instant ice packs for treating injuries. Solid ammonia nitrate is contained inside a thin-walled plastic bag, which is sealed inside a thicker bag that also contains some water. The inner bag can be broken by pressing the outer bag, thereby allowing the ammonium nitrate to form a solution with the water which gets quite cold.)... 

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