Energy changes during chemical reactions are very important to understand how these reactions work.

Let’s break it down:

1. Exothermic Reactions:

   • These reactions give off energy, usually in the form of heat.
   • For example, when fuels burn, they release a lot of energy—often more than $-1000 \, \text{J}$ for every mole.

2. Endothermic Reactions:

   • These reactions take in energy from their surroundings.
   • A good example is photosynthesis, where plants need about $2800 \, \text{J}$ of energy for each mole.

By learning about these energy changes, we can better predict how reactions will behave and how well they will work.