Chemicals can react in very different ways. Some chemical reactions produce energy and some of them absorb it.
Chemical reactions that absorb energy are called endothermic reactions. Plants that use photosynthesis to produce sugar absorb light energy from the sun. The chemical reaction of photosynthesis is considered endothermic because energy is absorbed during the reaction.
Chemical reactions that produce energy are called exothermic reactions. When firewood is burned in a fireplace and exothermic reaction takes place. Wood in the fire is burned in a chemical reaction that produces energy.
When acids and bases take part in a chemical reaction it is known as an acid-base reaction. Acids and bases that interact neutralize one another. Bases reduce the acidic qualities of acid, while acid reduces the basic properties of bases.
An example of an exothermic reaction: