Cold packs release cold is not an endothermic reaction as it absorbs heat from the surroundings.
Endothermic reaction is a reaction that absorbs heat from the surrounding to form a product .the entropy of the surrounding decreases.in endothermic reaction enthalpy change is positive.since hot packs release heat it involves endothermic reaction.it is a type of enterogenic reaction.it involves decrease in temperature as it absorb heat from the enviroment.it stores energy in the form of reaction.bond breaking requires energy while bond making release energy.Enthalpy change is the amount of energy absorbed in a reaction carried out at a constant pressure.Entropy is the measure of the disorder of the system.this explains hotpack release hot is a endothermic reaction and cold pack won't release cold.
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