Endothermic reactions are special chemical reactions that take in energy from their surroundings, mostly in the form of heat. Because of this, they make the area around them feel cooler.

How Endothermic Reactions Work:

1. Energy Needs:

   • Endothermic reactions need energy to break the bonds of the molecules that react with each other. This energy mostly comes from heat in the environment.

2. Energy Change:

   • In endothermic reactions, the overall energy change is positive. This means that the energy of the products is higher than that of the reactants. You can think of this as: $\Delta H > 0$
   • Here, $\Delta H$ shows us how much the energy has changed.

3. Examples:

   • Photosynthesis: Plants take in sunlight to change carbon dioxide and water into sugar (glucose) and oxygen. The reaction looks like this: $6CO_2 + 6H_2O + \text{sunlight} \rightarrow C_6H_{12}O_6 + 6O_2$
   • Dissolving Ammonium Nitrate: When ammonium nitrate ($NH_4NO_3$) mixes with water, it takes in heat, and this makes the water feel colder.

4. Uses:

   • Endothermic reactions are helpful in instant cold packs. When you activate the pack, it absorbs heat from its surroundings, which helps numb injuries.

In short, endothermic reactions are important in many natural and human-made processes. They take in energy and change the temperature around them.