Tearing a sheet of paper is classified as a physical change. Understanding this action requires looking at the fundamental scientific distinction between physical changes and chemical changes. This classification is a foundational concept in chemistry, helping to categorize the transformations that happen to materials. The difference centers on whether the material’s underlying chemical identity is permanently altered during the process.
Defining Physical and Chemical Changes
A physical change alters the form, size, or appearance of a substance but does not change its chemical composition. These changes involve moving molecules around without changing their internal structure or bonding. For example, melting ice or crushing a rock are changes in state or shape, but the substance remains chemically the same. Physical changes are often reversible and do not result in the formation of a new type of matter.
Conversely, a chemical change results in the formation of one or more new substances with entirely different chemical properties than the starting materials. This transformation, also known as a chemical reaction, involves the breaking and forming of chemical bonds between atoms. Chemical changes are typically irreversible. Evidence of a chemical change often includes a change in color, the production of gas, or the release of light and heat.
Why Tearing Paper is a Physical Change
The act of tearing paper represents a physical deformation, where the size and shape of the material are altered, but its molecular identity is preserved. Paper is primarily composed of long chains of cellulose, a carbohydrate polymer with the general chemical formula (C6H10O5)n. These fibers are held together in a sheet by a network of weak intermolecular forces, most notably hydrogen bonds.
When a piece of paper is torn, the mechanical force only breaks these weak hydrogen bonds and other physical connections between the cellulose fibers. The chemical structure of the cellulose molecules themselves remains completely intact. No new substance is created, and the fundamental chemical composition of the paper is unchanged, fitting the definition of a physical change. This is similar to crushing a piece of aluminum foil, which changes its shape but leaves the aluminum atoms unaltered.
Contrasting Tearing Paper with Burning Paper
The difference between a physical and a chemical change becomes clear when comparing tearing paper to burning it. Burning paper is an example of a chemical change called combustion. This process involves the paper’s cellulose and other organic components reacting vigorously with oxygen from the air.
During combustion, the chemical bonds within the cellulose molecules are broken, and the atoms rearrange to form entirely new substances. The primary products are carbon dioxide (CO2) gas and water vapor (H2O), which escape as smoke. A solid residue, known as ash, is also left behind, consisting of unburnt carbon and inorganic materials. These products are chemically distinct from the original paper, confirming that the material’s identity has been fundamentally altered. The process is irreversible.