Cold pack

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An (instant) cold pack or an (instant) cold compress is a bag that draws heat from the environment by cooling it down. Unlike ice packs and hot and cold compresses have cold packs not first be cooled, since they do not need the existing heat to warm up the pack, but for a endothermic reaction .

Working principle

Cold packs use chemical compounds with a positive enthalpy of dissolution , for example ammonium nitrate or urea , which are dissolved in water and thus extract energy from it and thus also from the environment.

A cold pack consists of two separate areas. In one of the areas there is a chemical compound or a mixture of different chemical compounds. In Germany, after the explosion at BASF 's Oppau nitrogen plant in Ludwigshafen-Oppau, no ammonium nitrate was used, only the more harmless calcium ammonium nitrate . Because of the EU regulation No. 98/2013 (raw materials for explosives), urea is used for cold packs in Europe today .

There is water in the other area. If the partition wall is destroyed by mechanical processes, the urea dissolves in the water. The lattice energy of the urea and the binding energy of the water have to be applied and the hydration energy is released. In the case of urea in the cold pack, the lattice energy and the binding energy are greater than the hydration energy, so the system extracts the difference between these energies from the environment.

Areas of application

Since the cold packs initially have a storage / ambient temperature and only become cold when the two components are mixed, they can, unlike cold packs, be stored longer at high ambient temperatures without losing their cooling effect, which only heats the environment through the chemical reaction withdraws. You will e.g. B. carried in first aid rucksacks to cool strains, bruises or inflammations.

Individual evidence

  1. ↑ Immediate cold pack size. L. In: Radecker Emergency Medicine, D-72119 Ammerbuch / Entringen, radecker-notfallmedizin.de. 2020, accessed April 1, 2020 .
  2. ↑ a b c d Just in time for the summer heat and the sports event: ice packs. In: Prof. Dr. Rüdiger Blume, Cornelsen Verlag GmbH, chemieunterricht.de. December 30, 2019, accessed April 1, 2020 .