Enthalpy change is important when looking at chemical reactions. It helps us understand how energy moves around during these processes.

There are two main types of reactions:

1. Exothermic reactions:

   • These reactions give off energy, usually as heat.
   • In this case, the enthalpy change (we write it as $\Delta H$) is negative. This means the energy of the final products is lower than the starting materials (reactants).
   • A well-known example is burning fuel, like in a fire, where heat is released.

2. Endothermic reactions:

   • These reactions take in energy from the surroundings.
   • Here, the enthalpy change is positive ($\Delta H > 0$). This means the products have more energy than the reactants.
   • A good example of this is photosynthesis. Plants absorb sunlight to convert carbon dioxide and water into glucose (sugar).

By understanding these changes, we can predict how energy moves in reactions. This knowledge is really helpful for studying chemistry!