Introduction
Reactions are extremely important as they reveal how substances change and transform. This article will outline the two types of reactions you will encounter–physical and chemical reactions–and explain how to identify them, which is an important foundation for later topics.
What is a Reaction? A reaction is a process where a substance changes. Specifically, a substance can either change its form or change its entire composition. When a reaction occurs, it is important to note that mass is conserved no matter the type of reaction.
Physical Reactions
A physical reaction is a type of reaction in which a substance changes its form, rather than changing its chemical composition. There is a key trait to note when identifying such reactions: no new substances are formed. There are different types of physical reactions, such as tearing or folding the substance and changing its texture, however phase changes (melting, boiling, etc.) are also types of physical reactions.
Ex: Ice melting
Ex: Cutting butter
Chemical Reactions
A chemical reaction is a process in which a substance changes its chemical composition, forming one or more new substances. There are many ways to tell whether a chemical reaction has occurred, including changes in color and/or odor; the production of heat, light, or gas, or the formation of a precipitate.
Ex: Iron rusting
Ex: Combustion of methane