Reactions are the processes that occur when substances interact with each other, leading to the formation of new substances. For example, when sodium reacts with water, it produces sodium hydroxide and hydrogen gas. This interaction can release energy, often in the form of heat or light, making reactions an essential part of chemistry. There are different types of reactions, such as combination, decomposition, and displacement reactions. Each type has its own unique characteristics and outcomes. Understanding these reactions helps scientists develop new materials, medicines, and technologies, showcasing the importance of chemistry in our daily lives.