Cutting paper is a physical change, not a chemical change. This simple action helps illustrate the fundamental difference between physical and chemical changes in matter, a distinction that relies on whether the material’s core identity is altered.
Defining Physical Change
A physical change is a transformation that affects the form or appearance of a substance but leaves its intrinsic chemical composition unchanged. The substance retains its original chemical identity, meaning the molecules themselves are not broken apart or rearranged to form a new compound. The change is primarily in physical properties, such as size, shape, state of matter, or texture.
Physical changes are often reversible and do not result in the creation of a new substance. Examples include melting ice into liquid water, dissolving salt in water, or crushing a piece of metal. In all these actions, the molecules or atoms remain chemically the same throughout the process.
Indicators of Chemical Change
A chemical change, also known as a chemical reaction, occurs when one or more substances are converted into entirely new substances with different chemical properties. This transformation involves the breaking and forming of chemical bonds at the molecular level. A chemical change is typically difficult or impossible to reverse using simple physical means.
Several observable signs suggest that a chemical reaction has taken place:
- The production of a gas, often seen as bubbling or fizzing.
- A spontaneous and irreversible change in color.
- The formation of a precipitate, a solid that separates from a liquid solution.
- A significant release or absorption of energy, manifesting as a change in temperature or the emission of light.
- The production of a distinct new odor.
Why Cutting Paper is a Physical Change
The act of cutting paper is a physical change because it alters only the size and shape of the original material. Paper is primarily composed of cellulose fibers, which are long chains of glucose molecules chemically bonded together. When scissors slice through a sheet, it breaks the physical connections between these fibers, but it does not break the chemical bonds within the cellulose molecules themselves.
The resulting smaller pieces of paper have the exact same chemical composition—they are still cellulose. None of the indicators of a chemical change are present during the cutting process. There is no change in color, gas production, precipitate formation, or significant heat or light generation. The change is strictly macroscopic, involving only the reduction in the material’s overall dimensions.
Chemical Reactions Involving Paper
While cutting paper is a physical change, paper is capable of undergoing several chemical reactions that fundamentally alter its composition.
Combustion
The most common and rapid example is combustion, or burning, which is a high-speed chemical reaction with oxygen. In this process, the cellulose rapidly reacts with atmospheric oxygen to produce entirely new substances: carbon dioxide gas, water vapor, and solid ash, which is mostly inorganic residue. This reaction is chemical because it releases both light and heat energy, and the resulting ash is chemically distinct from the original paper.
Aging and Yellowing
A slower chemical change involving paper is the process of aging, often seen as the yellowing or browning of old newspapers and books. This discoloration is largely due to the oxidation of lignin, a component present in wood pulp that is more reactive than cellulose. Lignin slowly reacts with oxygen and light over time, leading to the formation of chromophores, which impart a yellow-brown color to the paper.