8.4 Lab: Designing a Hand Warmer

AP Chemistry



A hand warmer consists of a plastic package containing a solid and an inner pouch filled with water. When the pack is activated, the solid dissolves in water and produces warmth. The energy or enthalpy change associated with the process of a solute dissolving in a solvent is called the heat of solution (ΔHsoln). At constant pressure, this enthalpy change is equal in magnitude to heat loss/gain, q, to the surroundings.

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Extrapolating from the information collected, calcium chloride can be used in an effective hand warmer because it can increase the temperature by at least 20 degrees celsius and it is nontoxic and safe for the environment. Calcium chloride is also economical because it costs $10.80 per kilogram, and we only need a small amount (1/10 of a kilogram). In each hand warmer, 0.01 kg of CaCl2 is needed, thus making each hand warmer cost $0.108 (negating the price of water and plastic bags).

Calculations: ($10.80 per kg x 0.01 kg CaCl2 = $0.108 per hand warmer).