Exothermic reactions play an important role in producing energy because they give off heat.

This happens when the energy in the products is less than the energy in the reactants. When this occurs, we say there’s a negative change in energy, or $\Delta H < 0$.

Here are some key points to show why these reactions matter:

1. Everyday Examples: When we burn fuels like wood, coal, or gasoline, we're using exothermic reactions. These fuels react with oxygen and let out heat. We use this heat for cooking food or warming our homes.

2. Industrial Uses: In factories, exothermic reactions help in making steam for power plants. The heat given off from burning fuels is used to turn turbines that generate electricity.

3. Importance in Our Bodies: Our bodies rely on a process called cellular respiration, which is also exothermic. When glucose (a type of sugar) combines with oxygen, it releases energy. We need this energy for everything, from moving around to thinking clearly.

In short, exothermic reactions are essential. They provide the energy we need for our daily lives and help meet larger energy demands in various industries.