Answer:
Explanation: A heat pack contains a mixture of chemicals that undergo an exothermic reaction when exposed to air or water. The reaction is typically initiated by breaking a capsule or squeezing the pack, which mixes the chemicals and starts the reaction.
The exothermic reaction produces heat as a byproduct, which is why the heat pack gets warm. The reaction is typically between iron powder and an oxidizing agent, such as activated carbon or vermiculite. When the oxidizing agent is exposed to air or water, it releases oxygen, which reacts with the iron powder to produce iron oxide and heat.
The reaction is exothermic because it releases heat to the surroundings. Exothermic reactions are characterized by a negative change in enthalpy, which means that the reactants have a higher energy level than the products. In the case of a heat pack, the reaction releases heat energy, which is transferred to the surroundings, making the pack warm.