A chemical reaction is a process where substances, called reactants, transform into new substances, known as products. This transformation involves breaking and forming bonds between atoms, leading to changes in the chemical structure. For example, when hydrogen gas reacts with oxygen gas, they form water, a completely different substance. Chemical reactions can be observed in everyday life, such as when baking soda reacts with vinegar to produce carbon dioxide gas, creating bubbles. These reactions can be classified into different types, like combination, decomposition, and displacement, each with unique characteristics and applications in fields like chemistry and medicine.