Final answer:
Chemical reactions alter the differences between the properties of substances, resulting in the formation of new substances with different properties.
Step-by-step explanation:
The main reason we use chemical reactions is to alter the differences between the properties of substances. Chemical reactions result in the formation of new substances with different properties than the reactants. For example, when hydrogen and oxygen react to form water, the properties of water like boiling point, density, and reactivity are different from those of hydrogen and oxygen.