As we get further and further into the winter season, the days will become colder as we go on. However, this does not stop athletes from going outside and participating in activities. Athletes try to tough it out through the harsh weather, but they still try to stay warm in any way that they can.
Over a variety of other items, one of the most convenient, popular, and easy to use is the hand warmer. Hand warmers utilize exothermic chemical reactions to produce heat that the user feels. There are a few different methods for this to happen, but the most common is a classic oxidation reaction that occurs in disposable hand warmers. The inside of the pouch consists of iron powder so when it is exposed to the air, it starts to rust. This reaction (4Fe + 3O2 → 2Fe2O3) is what produces the heat that the user feels. Some other ingredients in the pouch are used to make the hand warmer more efficient. Carbon is used to spread the heat out more evenly and a compound called vermiculite is used to help insulate the pouch to keep it warm for a longer period of time.
The other type of hand warmer is a reusable pouch with a liquid and small disk inside. Once the disk is pushed, the liquid appears to freeze and the pouch gets warm. This is because the liquid is supersaturated sodium acetate (CH3COONa) and is able to crystallize once the disk is crushed. The bonding process for the sodium acetate to become sodium acetate trihydrate (shown below) crystals is exothermic and that is why heat can be felt. These crystals also have the distinct and advantageous property to be able to melt at relatively low temperatures. Sodium acetate trihydrate can melt into its water of crystallization at around 58°C and can even be allowed to cool and remain in this state if it is heated to 100°C. This allows it to be reused over and over again and why hand warmers are so useful.